tcp: small optimization when TCP_TW_SYN is processed

When TCP_TW_SYN is processed, we perform a lookup to find
a listener and jump back in tcp_v6_rcv() and tcp_v4_rcv()

Paolo suggested that we do not have to check if the
found socket is a TIME_WAIT or NEW_SYN_RECV one.
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Link: https://lore.kernel.org/netdev/68085c8a84538cacaac991415e4ccc72f45e76c2.camel@redhat.com/Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Link: https://lore.kernel.org/r/20240411082530.907113-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_ipv4.c

@@ -2205,7 +2205,6 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	if (!sk)
 		goto no_tcp_socket;
 
-process:
 	if (sk->sk_state == TCP_TIME_WAIT)
 		goto do_time_wait;
 
@@ -2285,6 +2284,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 		}
 	}
 
+process:
 	if (static_branch_unlikely(&ip4_min_ttl)) {
 		/* min_ttl can be changed concurrently from do_ip_setsockopt() */
 		if (unlikely(iph->ttl < READ_ONCE(inet_sk(sk)->min_ttl))) {

net/ipv6/tcp_ipv6.c

@@ -1794,7 +1794,6 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
 	if (!sk)
 		goto no_tcp_socket;
 
-process:
 	if (sk->sk_state == TCP_TIME_WAIT)
 		goto do_time_wait;
 
@@ -1871,6 +1870,7 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
 		}
 	}
 
+process:
 	if (static_branch_unlikely(&ip6_min_hopcount)) {
 		/* min_hopcount can be changed concurrently from do_ipv6_setsockopt() */
 		if (unlikely(hdr->hop_limit < READ_ONCE(tcp_inet6_sk(sk)->min_hopcount))) {