Neutron host extension

Provide interfaces for the host Neutron extension API

Change-Id: Ia62884310c7a39db5e5df45707612d9b6a6181e7
Signed-off-by: Ryu Ishimoto <ryu@midokura.com>
Bump the Host version to v2

Host version v1 is going to be deprecated.  Bump to v2.

Change-Id: I163db7b00cfc0ca8c0cfd6c00da80dd895ff97e7
Signed-off-by: Ryu Ishimoto <ryu@midokura.com>