syscall: NetlinkRIB creates AF_NETLINK socket without SOCK_CLOEXEC

[lmb]

syscall.NetlinkRIB (which is used by net.InterfaceByName, etc.) creates an AF_NETLINK socket without setting SOCK_CLOEXEC. This means fork / exec will leak this socket to child processes.

LsfSocket and SetLsfPromisc are also affected by this, but are marked as deprecated.

What version of Go are you using (go version)?

$ go version
go version go1.13.3 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

Linux

[gopherbot]

Change https://golang.org/cl/210517 mentions this issue: syscall: use SOCK_CLOEXEC when creating sockets

[toothrot]

/cc @ianlancetaylor @bradfitz