tcp: ulp: fix possible crash in tcp_diag_get_aux_size()

tcp_diag_get_aux_size() can be called with sockets in any state.

icsk_ulp_ops is only present for full sockets.

For SYN_RECV or TIME_WAIT ones we would access garbage.

Fixes: 61723b39

 ("tcp: ulp: add functions to dump ulp-specific information")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Luke Hsiao <lukehsiao@google.com>
Reported-by: Neal Cardwell <ncardwell@google.com>
Cc: Davide Caratti <dcaratti@redhat.com>
Acked-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>