Support for IP_FREEBIND on Linux

[redactedontop]

Is your feature request related to a problem? Please describe.
It's really annoying to have to use socket2 (and SockRef::from(&socket)) just to change freebind, especially as TcpSocket wraps it.

Describe the solution you'd like
I'd like 2 methods like set_nodelay, but for freebind on Linux (IPv4 and IPv6).

Describe alternatives you've considered
Don't see any.

Additional context
socket2's implementation with a cfg to allow the function based on OS (preferably do the same)