Make OVS controller inactivity_probe configurable

This parameter applies to the OVSDB Controller table when the
native openflow driver is used. There are reports that increasing
it can reduce errors on busy systems.
See the ovs-vswitchd.conf.db man page for full description.

Change-Id: Ide829cad46d3aff7db0fe9e0d85f95b92931a38b
Related-Prod: PROD-30984
Related-Prod: PROD-28559
diff --git a/README.rst b/README.rst
index 2ef3f49..db33797 100644
--- a/README.rst
+++ b/README.rst
@@ -1509,6 +1509,7 @@
       gateway:
         of_connect_timeout: 60
         of_request_timeout: 30
+        of_inactivity_probe: 30
         ovs_vsctl_timeout: 30  # Pike
         ovsdb_timeout: 30  # Queens and beyond
         bridge_mac_table_size: 100000