Enhancement: Allow configuration of inactivity_probe and max_backoff for OVS

Echo request from OVS uses default value today, which is 5 seconds. In scale setups, Full GC can take more than 5 seconds which will result in a disconnection from all OVSs.
To control this behavior, inactivity_probe can be increased when creating a bridge.
OVSDB already created a patch that will allow its clients to define their desired inactivity_probe:
https://git.opendaylight.org/gerrit/#/c/50643/

Now Netvirt needs to expose an ability to configure this externally.