Merge branch 'tunnels'

Pravin B Shelar says:

====================
Following patch series restructure GRE and IPIP tunneling code
to make it modular. It adds ip_tunnel module which acts as
generic tunneling layer which has common code.

These patches do not change any functionality.
v3:v4:
 - Fixed compilation error in ipv6.
 - Few coding style fixes.
v2-v3:
 - Use GPL exports for all export symbols.
 - Set default config NET_IP_TUNNEL to m.
v1-v2:
 - Dropped patch to convert gre_proto_lock to rtnl lock.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>