The previous code was validating the netlink family incorrectly.
The module also forces no Netlink family collissions now; it used
to shrug them off, accepting that one of the modules would get
no requests from userspace.
Improves the fix to #224.
These arguments (to the userspace app and the kernel module,
respectively) will let the user decide which families the Netlink
sockets should be bound to.
This allows a SIIT and a NAT64 to coexist in a namespace bumplessly.
The arguments are Jool 3.4 only. Jool 3.5 will not need to concern
itself with Netlink.