mptcp: optimize the input options processing

Most MPTCP packets carries a single MPTCP subption: the
DSS containing the mapping for the current packet.

Check explicitly for the above, so that is such scenario we
replace most conditional statements with a single likely() one.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/options.c

@@ -1111,13 +1111,15 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 	if (!check_fully_established(msk, sk, subflow, skb, &mp_opt))
 		return sk->sk_state != TCP_CLOSE;
 
+	if (unlikely(mp_opt.suboptions != OPTION_MPTCP_DSS)) {
 		if ((mp_opt.suboptions & OPTION_MPTCP_FASTCLOSE) &&
 		    msk->local_key == mp_opt.rcvr_key) {
 			WRITE_ONCE(msk->rcv_fastclose, true);
 			mptcp_schedule_work((struct sock *)msk);
 		}
 
-	if ((mp_opt.suboptions & OPTION_MPTCP_ADD_ADDR) && add_addr_hmac_valid(msk, &mp_opt)) {
+		if ((mp_opt.suboptions & OPTION_MPTCP_ADD_ADDR) &&
+		    add_addr_hmac_valid(msk, &mp_opt)) {
 			if (!mp_opt.echo) {
 				mptcp_pm_add_addr_received(msk, &mp_opt.addr);
 				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDR);
@@ -1152,6 +1154,7 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 
 		if (!(mp_opt.suboptions & OPTION_MPTCP_DSS))
 			return true;
+	}
 
 	/* we can't wait for recvmsg() to update the ack_seq, otherwise
 	 * monodirectional flows will stuck
@@ -1179,7 +1182,7 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 
 	memset(mpext, 0, sizeof(*mpext));
 
-	if (mp_opt.use_map) {
+	if (likely(mp_opt.use_map)) {
 		if (mp_opt.mpc_map) {
 			/* this is an MP_CAPABLE carrying MPTCP data
 			 * we know this map the first chunk of data