selftests: net: Fix bridge backup port test flakiness

The test toggles the carrier of a bridge port in order to test the
bridge backup port feature.

Due to the linkwatch delayed work the carrier change is not always
reflected fast enough to the bridge driver and packets are not forwarded
as the test expects, resulting in failures [1].

Fix by busy waiting on the bridge port state until it changes to the
desired state following the carrier change.

[1]
# Backup port
# -----------
[...]
# TEST: swp1 carrier off [ OK ]
# TEST: No forwarding out of swp1 [FAIL]
[ 641.995910] br0: port 1(swp1) entered disabled state
# TEST: No forwarding out of vx0 [ OK ]

Fixes: b408453053fb ("selftests: net: Add bridge backup port and backup nexthop ID test")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20240208123110.1063930-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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

There is no h1 h2 actually. Remove it. Here is the test result after
conversion.

]# ./test_bridge_backup_port.sh

Backup port
-----------
TEST: Forwarding out of swp1 [ OK ]
TEST: No forwarding out of vx0 [ OK ]
TEST: swp1 carrier off [ OK ]
TEST: No forwarding out of swp1 [ OK ]
...
Backup nexthop ID - ping
------------------------
TEST: Ping with backup nexthop ID [ OK ]
TEST: Ping after disabling backup nexthop ID [ OK ]

Backup nexthop ID - torture test
--------------------------------
TEST: Torture test [ OK ]

Tests passed: 83
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 backup port and backup nexthop ID test

Add test cases for bridge backup port and backup nexthop ID, testing
both good and bad flows.

Example truncated output:

# ./test_bridge_backup_port.sh
[...]
Tests passed: 83
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>