selftests: net: Add bridge neighbor suppression test

Add test cases for bridge neighbor suppression, testing both per-port
and per-{Port, VLAN} neighbor suppression with both ARP and NS packets.

Example truncated output:

 # ./test_bridge_neigh_suppress.sh
 [...]
 Tests passed: 148
 Tests failed:   0

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>