MPLS label rebake for multicast was done when label changes. However rebake should be done
whenever there is a change in component NH to which label points.
e.g. if interface gets added in interface comp NH mpls label was not getting updated with new comp NH
as it saw this operation as no-op bcoz there was no label change.

Code change fixes this scenario and rebakes label with comp NH everytime.
Old label is deleted only when label changes.

Change-Id: I18df452867e2f0890aae1800b20e61facd382e55
Merge "MPLS label rebake for multicast was done when label changes. However rebake should be done whenever there is a change in component NH to which label points. e.g. if interface gets added in interface comp NH mpls label was not getting updated with new comp NH as it saw this operation as no-op bcoz there was no label change."