sock_diag: add module pointer to "struct sock_diag_handler"

[ Upstream commit 114b4bb1 ]

Following patch is going to use RCU instead of
sock_diag_table_mutex acquisition.

This patch is a preparation, no change of behavior yet.

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>
Stable-dep-of: eb02688c ("ipv6: release nexthop on device removal")
Signed-off-by: Sasha Levin <sashal@kernel.org>