As stated in the bug description, there are many writes of the
agent liveness external_ids into the Chassis table. There was a
protection to avoid bumping nb_cfg too frequently.
The same protection is reused to avoid writing into the Chassis
external_ids.
This patch reduces the number of transactions to the SB database
and, therefore, the recomputations that it causes to ovn-controller
in all nodes.
Change-Id: I5db90fde8e7394772ec23c6384c711096c246621
Closes-Bug: #1883554
Signed-off-by: Daniel Alvarez <dalvarez@redhat.com>