ip: ipnexthop: Support dumping next hop group HW stats

ip: ipnexthop: Support dumping next hop group HW stats

Besides SW datapath stats, the kernel also support collecting statistics
from HW datapath, for nexthop groups offloaded to HW. Request that these be
collected when ip is given "-s -s", similarly to how "ip link" shows more
statistics in that case.

Besides the statistics themselves, also show whether the collection of HW
statistics was in fact requested, and whether any driver actually
implemented the request.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>