lib: copy_nexthops() only copies the first nexthop

lib: copy_nexthops() only copies the first nexthop

Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
Before the fix NHT had each path resolving via swp1

cel-redxp-10# show ip route 20.0.11.253
Routing entry for 20.0.11.0/24
  Known via "bgp", distance 20, metric 0, best
  Last update 00:00:20 ago
  * 169.254.0.1, via swp1
  * 169.254.0.17, via swp2

cel-redxp-10#

cel-redxp-10# show ip nht
[snip]
20.0.11.253
 resolved via bgp
 via 169.254.0.1, swp1
 via 169.254.0.1, swp1
 Client list: pim(fd 19)

After the fix

cel-redxp-10# show ip nht
[snip]
20.0.11.253
 resolved via bgp
 via 169.254.0.1, swp1
 via 169.254.0.17, swp2
 Client list: pim(fd 19)