Add tunnelzone extension

This patch adds tunnelzone extension and unit tests for tunnelzone
extension.

Change-Id: I085977e56928003e0421b1f210386fec8731a493
Signed-off-by: Taku Fukushima <tfukushima@midokura.com>
Add methods required for the plugin

Change-Id: Ifca07bf17ac9c7e946101ff665f3aef310949e30
Signed-off-by: Taku Fukushima <tfukushima@midokura.com>