bgpd: Fix attribute handling upon redistribution metric change

bgpd: Fix attribute handling upon redistribution metric change

When the metric for a redistributed route is changed through configuration,
the path attribute for the route/routes need to be "re-created" as the hash
entry would change. In the absence of this, the entry would have the correct
values but when a hash lookup is done at a later time (e.g., when trying to
free the entry), it would fail. This patch addresses the "re-creation"

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Ticket: CM-11168
Reviewed By: CCR-4990
Testing Done: Manual, bgp-smoke