BGP: Display the interface name used to resolve a nexthop.

BGP: Display the interface name used to resolve a nexthop.

Display the interface name used to resolve a nexthop instead of just
the ifIdx. This is already done for many cases, but was missing for
one scenario.

Signed-off-by: Vivek Venkataraman <vivek@cumulusnetworks.com>
Reviewed-by: Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by: Daniel Walton <dwalton@cumulusnetworks.com>
Ticket: CM-6888
Reviewed By: CCR-3705
Testing Done: Manual verification

This is an import of patch bgpd-show-ifname-for-nht.patch from 2.5-br.