Inconsistent key of bridge_macs in provider app

[gospring]

In provider app _setup_physical_bridges function, self.bridge_macs use physical network name as key. But in _update_bridge_mac function, we use ovsport.name as key to find result in
self.bridge_macs

if bridge not in self.bridge_macs:
    return

so bridge not in self.bridge_macs will be always true.