bgpd: Use source route's path attributes for type-5 routes

bgpd: Use source route's path attributes for type-5 routes

When an IPv4 or IPv6 unicast route is injected into EVPN as a type-5 route
(upon user configuration), ensure that the source route (best path)'s path
attributes are used to build the EVPN type-5 route. This will result in
correct AS_PATH and ORIGIN attributes for the type-5 route so that it doesn't
appear that all type-5 routes are locally sourced. This is necessary to
ensure that external paths (IPv4 or IPv6 from EBGP peer) are preferred over
internal EVPN paths, if both exist.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Ticket: CM-19051
Reviewed By: CCR-7009
Testing Done: Verify failed scenario