Comment 22 for bug 1574169

Reviewed: https://review.opencontrail.org/19717
Committed: http://github.org/Juniper/contrail-controller/commit/e62159cce888819c0d67803466fc1a5fead3db29
Submitter: Zuul
Branch: R2.21.x

commit e62159cce888819c0d67803466fc1a5fead3db29
Author: Prakash Bailkeri <email address hidden>
Date: Tue Apr 26 16:33:41 2016 +0530

Race condition between route handling and VRF subscription

As part of fix for 1563550, fix for one corner case is missed.

Consider the case where
1. route add operation is enqueued to DB,
2. unsubscribe for the instance is received,
3. membership manager API to unregister table is called, membership managers
starts leave and part of the table is walked but membership manager has not
yet removed IPeerRib,
4. Route add request is processed and path gets added.

Fix:
1. Reset the subscription gen id when unregister request is handled. i.e.
before starting the walk. This will ensure that delayed route add is rejected.

2. Add UT cases to validate above mentioned scenario

Change-Id: Ic12259b852227c1f199a67611da49a3563010026
Closes-Bug: #1574169
(cherry picked from commit 315c60bca45710d8ef9de2bc0ff123316d9ea3db)