net: Fix inverted test in __skb_recv_datagram

As the kernel generally uses negated error numbers, *err needs to be
compared with -EAGAIN (d'oh).

Signed-off-by: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Fixes: ea3793ee29d3 ("core: enable more fine-grained datagram reception control")
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/datagram.c

@@ -275,7 +275,7 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
 		if (skb)
 			return skb;
 
-		if (*err != EAGAIN)
+		if (*err != -EAGAIN)
 			break;
 	} while (timeo &&
 		!__skb_wait_for_more_packets(sk, err, &timeo, last));