openvswitch: only init bridges when (re)starting

openvswitch: only init bridges when (re)starting

Calling the ovs_bridge_init function when stopping the service will
result in ovs-vsctl being called after ovsdb-server has been shut down.
This causes the following error:

ovs-vsctl: unix:/var/run/openvswitch/db.sock: database connection failed (No such file or directory)

Calling the ovs_bridge_init function when requesting the service status
has no added value.

Only call ovs_bridge_init during start or restart to fix this.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>