tcp: make tcp_rcv_state_process() drop monitor friendly

tcp_rcv_state_process() incorrectly drops packets
instead of consuming it, making drop monitor very noisy,
if not unusable.

Calling tcp_time_wait() or tcp_done() is part
of standard behavior, packets triggering these actions
were not dropped.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -6580,7 +6580,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 			inet_csk_reset_keepalive_timer(sk, tmo);
 		} else {
 			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
-			goto discard;
+			goto consume;
 		}
 		break;
 	}
@@ -6588,7 +6588,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 	case TCP_CLOSING:
 		if (tp->snd_una == tp->write_seq) {
 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
-			goto discard;
+			goto consume;
 		}
 		break;
 
@@ -6596,7 +6596,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		if (tp->snd_una == tp->write_seq) {
 			tcp_update_metrics(sk);
 			tcp_done(sk);
-			goto discard;
+			goto consume;
 		}
 		break;
 	}
@@ -6650,6 +6650,10 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		tcp_drop(sk, skb);
 	}
 	return 0;
+
+consume:
+	__kfree_skb(skb);
+	return 0;
 }
 EXPORT_SYMBOL(tcp_rcv_state_process);