This fixes race condition leading to lack of fdb entries
on agent after OVS restart, if agent managed to handle all ports
before sending state report with start_flag set to True.
Change-Id: I943f8d805630cdfbefff9cff1fb4bce89210618b
Closes-Bug: #1808136
(cherry picked from commit 3995abefb16181594181133b271cdf35fa8d9937)