Initial support for vxlan on linuxbridge.

blueprint vxlan-linuxbridge

Linux kernel starting from 3.7 offer native support for vxlan. This is
initial implementation of this feature in quantum for linuxbridge.

Change-Id: I7c6558c3fd890ca76d5dea02ddab005470aa787c
fixes for ip_lib

Change-Id: I51c4183e2794197073baed5b885099992fdc62f2
split vlan_ranges to vlan_ranges and vni_ranges

Change-Id: If53d108640a27d10b43ac8b6424bc5b588eae710
network_type in network_states

Change-Id: Idbe5b61442dcabd5a2f9af4e51380ce8bf2ffc6b