Update `mptcp_upstream.h' to the latest upstream version of
<linux/mptcp.h>.

In `src/netlink_pm_upstream.c', include <mptcpd/addr_info.h> before
<mptcpd/private/mptcp_upstream.h> to avoid redefinition of the same
symbols.  The symbols in question, such as struct in_addr, are found
in both <netinet/in.h> and <linux/in.h>.  The former is included in
<mptcpd/addr_info.h> and the latter is included in a recent version of
<linux/mptcp.h>.  Reording the include directives allows the C library
compatibility logic in <linux/libc-compat.h> included by <linux/in.h>
to detect a previous include of <netinet/in.h> to avoid redefinition
of symbols.

Display the kernel supported by mptcpd in the "--help" command line
option output, e.g.:

Usage: mptcpd [OPTION...]
Start the Multipath TCP daemon.
...
  -?, --help                 Give this help list
      --usage                Give a short usage message
  -V, --version              Print program version
...
Supported Linux kernel: upstream
...

The MPTCP listener manager maps MPTCP local address IDs to a file
descriptor for an open MPTCP listening socket.

Mptcpd now requires the MPTCP_ATTR_SERVER_SIDE enumerator to exist in
the upstream kernel <linux/mptcp.h> header.  Update the header
detection logic accordingly.

Propagate the MPTCP_ATTR_SERVER_SIDE attribute value to plugin
new_connection and connection_established operations.

Mptcpd plugin new_connection and connection_established operations now
accept a boolean "server_side" parameter.  Update mptcpd plugin
implementations accordingly.

Add the new "server_side" argument to all calls to test plugin
new_connection and connection_established operations.

Make the relationship between two duplicate sets of test plugin call
arguments by initializing the second set in terms of the first rather
than simple cut-n-paste initialization.  This minimizes potential for
argument mismatches between the two by only requiring changes to the
arguments in one place instead of two.  It also improve code
self-documentation.

Move struct sockaddr hash code out of `id_manager.c' and in to a
separate source and header file so that it may be used by other
hash maps in libmptcpd.

Verify that mptcpd_idm_map_id() correctly rejects an invalid (zero)
MPTCP address ID.

Map sockaddrs to file descriptors instead of MPTCP address ID to file
descriptor.  Reference count listeners as well to allow sharing.

A sockaddr is now needed to close a listener.  Add a sockaddr
parameter to mptcpd_pm_remove_addr(), accordingly.

Hash the IP port as part of the key to ensure the resulting key hash
is different between sockaddrs with the same IP address but different
ports.

This is necessary because the mptcpd listener manager would otherwise
only create listeners for a given IP address once even if the port
differs in subsequent mptcpd_lm_listen() calls.

Add an implicitly initialized dummy padding member to the hash key
structures, and drop the unions.  This is simpler than the previous
union based approach.

Add test cases for non-zero IP ports to the test-listener-manager
unit test.

Verify that getting the MPTCP address ID for sockaddrs containing the
same IP address but different ports results in the same ID.  Only the
IP address should be considered by the mptcpd ID manager.

The mptcpd ID manager and listener manager each have specific sockaddr
hashing requirements, where the former does not need the IP port and
the latter does.  Attempting to make a single hash implementation
support both cases was clumsy.  The mptcpd ID manager and listener
manager will each implement their own hash functions.  Common sockaddr
hashing related functions still exist in hash_sockaddr.[hc].

Only one instance of a mptcpd listener manager should be created.
That instance should be managed by the mptcpd core.  Make the
mptcpd_lm_create() and mptcpd_lm_destroy() part of the private mptcpd
API.

Allow the user to get access to the global mptcpd listener manager by
adding a new mptcpd_pm_get_lm() function to the public API.

Co-authored-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

Track the kernel assigned ephemeral port if the user provided a
sockaddr with a zero port to mptcpd_lm_listen(), and return that port
to the user.  The user is expected to pass a sockaddr with the port
returned from mptcpd_lm_listen() in a subsequent call to
mptcpd_lm_close().  Passing a sockaddr with a zero port to
mptcpd_lm_close() will result in failure since the listener manager
now only tracks listeners with non-zero addresses.

Reject unbound IP addresses such as INADDR_ANY, INADDR_BROADCAST, and
in6addr_any.  The mptcpd listener manager requires addresses to be
bound to a network interface.

Verify that the mptcpd listener manager rejects addresses that are not
bound to a network interface, i.e. INADDR_ANY, INADDR_BROADCAST, and
in6addr_any.

In some cases it is useful to copy the contents of a sockaddr based on
the address family.  Add a new mptcpd_sockaddr_copy() function that
does so.  Only AF_INET and AF_INET6 address families are supported.

The mptcpd_pm_add_addr() function now expects a pointer to a non-const
struct sockaddr.  Update the sspi plugin accordingly.

Overhaul the test-commands unit test with the following notable
changes:
    * Use different addresses for user and kernel space address
      advertising related commands.  This is needed to prevent
      listening on the same TCP address and port.
    * Use the same local and remote addresses for all user space
      subflow related commands.
    * Log addresses obtained from mptcpd_kpm_get_addr().

Split kernel and user space test cases to make it easier to determine
causes of failure.  The code is also cleaner with the split.

Propagate errors to callers by returning 0 on success, and -1 or errno
on error.  This allows for better error handling and diagnostics.

The EADDRNOTAVAIL error will generally occur during a call to
mptcpd_pm_add_addr() if the test is run without sufficient
capabilities (CAP_NET_ADMIN) to set up the test addresses by
associating them with a network interface.  Ignore the failure for
now.