BGP: Do appropriate cleanup on receipt of redistribute update

BGP: Do appropriate cleanup on receipt of redistribute update

When there is a change to a redistributed route, either an attribute
such as the metric or the route type itself has changed, protocol clients
receive an update of the route instead of a delete and add as a result
of an earlier optimization. The update needs to be handled as an implicit
delete for any existing redistributed route, especially to handle change
in route type.

Signed-off-by: Vivek Venkataraman <vivek@cumulusnetworks.com>
Reviewed-by: Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by: Daniel Walton <dwalton@cumulusnetworks.com>
Ticket: CM-7578
Reviewed By: CCR-3718
Testing Done: Manual verification
Related-to: CM-6768