iproute: Parse last nexthop in a multipath route

iproute: Parse last nexthop in a multipath route

Continue parsing a multipath payload as long as another nexthop can fit
in the payload.

# ip route add 192.0.2.0/24 nexthop dev dummy0 nexthop dev dummy1

Before:
# ip route show 192.0.2.0/24
192.0.2.0/24
        nexthop dev dummy0 weight 1

After:
# ip route show 192.0.2.0/24
192.0.2.0/24
        nexthop dev dummy0 weight 1
        nexthop dev dummy1 weight 1

Fixes: f48e14880a0e ("iproute: refactor multipath print")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>