Comment 23 for bug 1574169

Reviewed: https://review.opencontrail.org/19718
Committed: http://github.org/Juniper/contrail-controller/commit/242296f5161a7567869d6b1628e2c8ede9cfe1c6
Submitter: Zuul
Branch: R2.20

commit 242296f5161a7567869d6b1628e2c8ede9cfe1c6
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)