net: add large ecmp group nexthop tests

net: add large ecmp group nexthop tests

Add a couple large ecmp group nexthop selftests to cover
the remnant fixed by d69100b8eee27c2d60ee52df76e0b80a8d492d34.

The tests create 100 x32 ecmp groups of ipv4 and ipv6 and then
dump them. On kernels without the fix, they will fail due
to data remnant during the dump.

Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>