In https://review.opendev.org/#/c/753824/ ovsdbapp adds the ability
to pass a "frozen" object to the RowEventHandler so that if a
transaction is started from the main thread that changes the row,
it won't step on the values that the Event is trying to process.
This patch backports the ovs_idl backend-specific
RowEventHandler which converts the row to a frozen_row.
(cherry picked from commit