ila: propagate error code in ila_output

This warning:
net/ipv6/ila/ila_lwt.c: In function ‘ila_output’:
net/ipv6/ila/ila_lwt.c:42:6: warning: variable ‘err’ set but not used [-Wunused-but-set-variable]

It looks like the code attempts to set propagate different error
values, but always returned -EINVAL.

Compile tested only. Needs review by original author.
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ila/ila_lwt.c

@@ -91,7 +91,7 @@ static int ila_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 
 drop:
 	kfree_skb(skb);
-	return -EINVAL;
+	return err;
 }
 
 static int ila_input(struct sk_buff *skb)