This avoids the OPERSTATE unknown when the bridge is brought up but the
members are not ready yet.
This will make OPERSTATE to down, enabling us to wait until we have
brought up completely all the members.
Signed-off-by: Raito Bezarius <masterancpp@gmail.com>
... and make bridge use it.
We also had to convert bridge back into a pair of services.
Downstreams want to depend on the bridge it self being configured
even if not necessarily all the members are up. e.g. don't want
to break ssh on lan if there's a misconfigured wlan device
