inet_diag_lock_handler() reads inet_diag_table[proto] locklessly.

Use READ_ONCE()/WRITE_ONCE() annotations to avoid potential issues.

Fixes: d523a328 ("[INET]: Fix inet_diag dead-lock regression")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>