zebra: Add internal support for route tags

Add internal support for a route tag to be applied to routes.
At this point in time, tags are not being used.

[forward ported by Cumulus]

Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
Signed-off-by: Piotr Chytła <pch@packetconsulting.pl>
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Edited-by: Paul Jakma <paul.jakma@hpe.com> - rebase conflicts
3 files changed