IPIP: IP in IP package support

IPIP: IP in IP package support

The package supports IP in IP by registering the ipip protocol handler

Following options are configurable
    -peeraddr (IPv4 remote address)
    -ipaddr (IPv4 local address)
    -ttl (time to live of encapsulating packet)
    -tos (type of service of encapsulating packet either inherit (outer header inherits the value of the inner header) or hex value)
    -df (don't fragment flag of encapsulating packet)
    -mtu (IPIP tunnel mtu)
    -tunlink (bind tunnel to this interface)
    -zone (firewall zone to which the IPIP tunnel will be added)

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42746 3c298f89-4303-0410-b956-a3cf2f4a3e73