ss: support closing inet sockets via SOCK_DESTROY.

ss: support closing inet sockets via SOCK_DESTROY.

This patch adds a -K / --kill option to ss that attempts to
forcibly close matching sockets using SOCK_DESTROY.

Because ss typically prints sockets instead of acting on them,
and because the kernel only supports forcibly closing some types
of sockets, the output of -K is as follows:

- If closing the socket succeeds, the socket is printed.
- If the kernel does not support forcibly closing this type of
  socket (e.g., if it's a UDP socket, or a TIME_WAIT socket),
  the socket is silently skipped.
- If an error occurs (e.g., permission denied), the error is
  reported and ss exits.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>