ceph: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
[idryomov@gmail.com: amended "Older OSDs" comment]
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index ad93342..8a4d375 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -430,6 +430,7 @@ static void ceph_sock_state_change(struct sock *sk)
 	switch (sk->sk_state) {
 	case TCP_CLOSE:
 		dout("%s TCP_CLOSE\n", __func__);
+		/* fall through */
 	case TCP_CLOSE_WAIT:
 		dout("%s TCP_CLOSE_WAIT\n", __func__);
 		con_sock_state_closing(con);