This way, the IP address / route handling between TUN devices and kernel
GTP can be shared, which will provide not only a unified codebase but
also a more consistent behavior.
This also paves the road for to use kernel GTP from sgsnemu in the future.
Related: OS#3214
Change-Id: Ic53a971136edd0d8871fbd6746d7b0090ce3a188
Extend the IP pool implementation to be able to manage both pools
of 32bit addresses (IPv4) as well as pools of 128bit addresses (IPv6)
Change-Id: Ib98cc4bf634d6be9a7bf8c03a24e629455fcafc8