net: diag: Support destroying TCP sockets.

net: diag: Support destroying TCP sockets.

This implements SOCK_DESTROY for TCP sockets. It causes all
blocking calls on the socket to fail fast with ECONNABORTED and
causes a protocol close of the socket. It informs the other end
of the connection by sending a RST, i.e., initiating a TCP ABORT
as per RFC 793. ECONNABORTED was chosen for consistency with
FreeBSD.

[cherry-pick of net-next c1e64e298b8cad309091b95d8436a0255c84f54a]

Change-Id: I728a01ef03f2ccfb9016a3f3051ef00975980e49
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>