selftests/net: convert test_bridge_neigh_suppress.sh to run it in unique namespace

Here is the test result after conversion.

]# ./test_bridge_neigh_suppress.sh

Per-port ARP suppression - VLAN 10
----------------------------------
TEST: arping [ OK ]
TEST: ARP suppression [ OK ]

...

TEST: NS suppression (VLAN 20) [ OK ]

Tests passed: 148
Tests failed: 0

Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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>