net/sched: act_tunnel_key: disambiguate metadata dst error cases

Metadata may be NULL for one of two reasons:
* Missing user input
* Failure to allocate the metadata dst

Disambiguate these case by returning -EINVAL for the former and -ENOMEM
for the latter rather than -EINVAL for both cases.

This is in preparation for using extended ack to provide more information
to users when parsing their input.

Signed-off-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_tunnel_key.c

@@ -143,10 +143,13 @@ static int tunnel_key_init(struct net *net, struct nlattr *nla,
 			metadata = __ipv6_tun_set_dst(&saddr, &daddr, 0, 0, dst_port,
 						      0, flags,
 						      key_id, 0);
+		} else {
+			ret = -EINVAL;
+			goto err_out;
 		}
 
 		if (!metadata) {
-			ret = -EINVAL;
+			ret = -ENOMEM;
 			goto err_out;
 		}