tcp: fix incorrect LOCKDROPPEDICMPS counter

commit 563d34d057 (tcp: dont drop MTU reduction indications)
added an error leading to incorrect accounting of
LINUX_MIB_LOCKDROPPEDICMPS

If socket is owned by the user, we want to increment
this SNMP counter, unless the message is a
(ICMP_DEST_UNREACH,ICMP_FRAG_NEEDED) one.

Reported-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_ipv4.c

@@ -369,11 +369,10 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 	 * We do take care of PMTU discovery (RFC1191) special case :
 	 * we can receive locally generated ICMP messages while socket is held.
 	 */
-	if (sock_owned_by_user(sk) &&
-	    type != ICMP_DEST_UNREACH &&
-	    code != ICMP_FRAG_NEEDED)
-		NET_INC_STATS_BH(net, LINUX_MIB_LOCKDROPPEDICMPS);
-
+	if (sock_owned_by_user(sk)) {
+		if (!(type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED))
+			NET_INC_STATS_BH(net, LINUX_MIB_LOCKDROPPEDICMPS);
+	}
 	if (sk->sk_state == TCP_CLOSE)
 		goto out;