esp: Fix error handling on layer 2 xmit.

esp_output_tail() and esp6_output_tail() can return negative
and positive error values. We currently treat only negative
values as errors, fix this to treat both cases as error.

Fixes: fca11ebde3f0 ("esp4: Reorganize esp_output")
Fixes: 383d0350f2cc ("esp6: Reorganize esp_output")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv4/esp4_offload.c

@@ -257,7 +257,7 @@ static int esp_xmit(struct xfrm_state *x, struct sk_buff *skb,  netdev_features_
 	esp.seqno = cpu_to_be64(xo->seq.low + ((u64)xo->seq.hi << 32));
 
 	err = esp_output_tail(x, skb, &esp);
-	if (err < 0)
+	if (err)
 		return err;
 
 	secpath_reset(skb);

net/ipv6/esp6_offload.c

@@ -286,7 +286,7 @@ static int esp6_xmit(struct xfrm_state *x, struct sk_buff *skb,  netdev_features
 	esp.seqno = cpu_to_be64(xo->seq.low + ((u64)xo->seq.hi << 32));
 
 	err = esp6_output_tail(x, skb, &esp);
-	if (err < 0)
+	if (err)
 		return err;
 
 	secpath_reset(skb);