ipv6: fix 4in6 tunnel receive path

Protocol for 4in6 tunnel is IPPROTO_IPIP. This was wrongly changed by
the last cleanup.

CC: Tom Herbert <tom@herbertland.com>
Fixes: 0d3c703a9d17 ("ipv6: Cleanup IPv6 tunnel receive path")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_tunnel.c

@@ -897,7 +897,7 @@ drop:
 
 static int ip4ip6_rcv(struct sk_buff *skb)
 {
-	return ipxip6_rcv(skb, IPPROTO_IP, &tpi_v4,
+	return ipxip6_rcv(skb, IPPROTO_IPIP, &tpi_v4,
 			  ip4ip6_dscp_ecn_decapsulate);
 }