[IPCOMP]: Fix reception of incompressible packets

I made a silly typo by entering IPPROTO_IP (== 0) instead of
IPPROTO_IPIP (== 4).  This broke the reception of incompressible
packets.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/xfrm4_tunnel.c

@@ -50,7 +50,7 @@ static const struct xfrm_type ipip_type = {
 
 static int xfrm_tunnel_rcv(struct sk_buff *skb)
 {
-	return xfrm4_rcv_spi(skb, IPPROTO_IP, ip_hdr(skb)->saddr);
+	return xfrm4_rcv_spi(skb, IPPROTO_IPIP, ip_hdr(skb)->saddr);
 }
 
 static int xfrm_tunnel_err(struct sk_buff *skb, u32 info)