zebra: Add initial framework to keep track of changed route-maps

zebra: Add initial framework to keep track of changed route-maps

Add some basic code for zebra to start to keep track
of route-maps that have changed.  At this point we
are not doing anything.  As we fix code to handle
route-maps better, code will be shifted around.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>