Filters _get_node_network() to bridge/OVSBridge types only (excludes physical
NICs, bonds), plus SDN vnets from _get_sdn_vnets(). vlan_aware: Linux bridge
reflects its bridge_vlan_aware config flag; OVS bridge always true; SDN vnet
always false (VLAN already fixed by the vnet's zone/tag).
4 new tests: bridge/vnet filtering, Linux bridge vlan_aware flag, OVS bridge
always vlan_aware, SDN vnet never vlan_aware. All 15 tests in the file pass.