doc: update driver feature support matrix
doc: update driver feature support matrix

Updates for:
* vni extension
* routes-control extension
* L2 support

Change-Id: If896f70b29c25993f1de4811b30d10d792cf2b6b

openstack/networking-bgpvpn,openstack/networking-bgpvpn,openstack/networking-bgpvpn