Comment 30 for bug 1529829

Reviewed: https://review.opencontrail.org/17412
Committed: http://github.org/Juniper/contrail-controller/commit/60ec422fadb8930a95e153191f2e459ff7db8e02
Submitter: Zuul
Branch: R2.20

commit 60ec422fadb8930a95e153191f2e459ff7db8e02
Author: Manish <email address hidden>
Date: Fri Jan 15 08:56:00 2016 +0530

Multicast traffic gets dropped.

Problem:
When all the VMI's are gone multicast object is deleted. However VN is still not
gone and meanwhile new VMI gets added. During this window where all VMI were
gone to new VMI gets added, olist for replication tree is received from
control-node. This update is neglected in absence of multicast object for same.
This results in no multicast tree.

Solution:
Retain multicast object till two conditions are met:
- All VMIS are gone
- VN is no more in use by multicast.

Change-Id: Ic18907cf371d5accfe170cc6b2d2427912fc0b54
Closes-bug: 1529829