[INET_DIAG]: Use inet_twsk() with TIME_WAIT sockets

The fields being accessed in inet_diag_dump are outside sock_common, the
common part of struct sock and struct inet_timewait_sock.

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>