net/key/af_key.c: add missing kfree_skb

At the point of this error-handling code, alloc_skb has succeded, so free
the resulting skb by jumping to the err label.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/key/af_key.c

@@ -3480,7 +3480,7 @@ static int pfkey_send_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
 
 	/* Addresses to be used by KM for negotiation, if ext is available */
 	if (k != NULL && (set_sadb_kmaddress(skb, k) < 0))
-		return -EINVAL;
+		goto err;
 
 	/* selector src */
 	set_sadb_address(skb, sasize_sel, SADB_EXT_ADDRESS_SRC, sel);