udp6: fix encap return code for resubmitting

The commit eb63f296 ("udp6: add missing checks on edumux packet
processing") used the same return code convention of the ipv4 counterpart,
but ipv6 uses the opposite one: positive values means resubmit.

This change addresses the issue, using positive return value for
resubmitting. Also update the related comment, which was broken, too.

Fixes: eb63f296 ("udp6: add missing checks on edumux packet processing")
Signed-off-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/udp.c

@@ -766,11 +766,9 @@ static int udp6_unicast_rcv_skb(struct sock *sk, struct sk_buff *skb,
 
 	ret = udpv6_queue_rcv_skb(sk, skb);
 
-	/* a return value > 0 means to resubmit the input, but
-	 * it wants the return to be -protocol, or 0
-	 */
+	/* a return value > 0 means to resubmit the input */
 	if (ret > 0)
-		return -ret;
+		return ret;
 	return 0;
 }