Identifying and ignoring uninterested SouthBound updates.

Identifying and ignoring uninterested SouthBound updates.

Neutron bundle relies heavily on the Southbound events, especially the updates for its basic operations.
Many updates, especially the Packet statistics updates from Interface table are fast and furious and we
end up processing a lot of it unneccessarily. Due to the current implementation philosophy of maintaining
absolutely minimum cache in the neutron bundle, it relies heavily on the existing network states. Hence
such updates ends up reaching various layers. Hence identifying those updates and ignoring them becomes
critical for the stability of the system.

Change-Id: I10eb492e6e16be7931ec094bfcff54cc6b8696d6
Signed-off-by: Madhu Venugopal <mavenugo@gmail.com>