xfrm: Restrict extended sequence numbers to esp

The IPsec extended sequence numbers are fully implemented just for
esp. So restrict the usage to esp until other protocols have
support too.

Signed-off-by: Steffen Klassert <[e-mail]>
Acked-by: Herbert Xu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/xfrm/xfrm_user.c

···
 	if (!rt)
 		return 0;
 
+	if (p->id.proto != IPPROTO_ESP)
+		return -EINVAL;
+
 	if (p->replay_window != 0)
 		return -EINVAL;