IPIP: Use ip-tunneling code.

Reuse common ip-tunneling code which is re-factored from GRE
module.
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/Kconfig

@@ -166,6 +166,7 @@ config IP_PNP_RARP
 config NET_IPIP
 	tristate "IP: tunneling"
 	select INET_TUNNEL
+	select NET_IP_TUNNEL
 	---help---
 	  Tunneling means encapsulating data of one protocol type within
 	  another protocol and sending it over a channel that understands the