selftests: forwarding: Fix bridge MDB test flakiness

selftests: forwarding: Fix bridge MDB test flakiness

After enabling a multicast querier on the bridge (like the test is
doing), the bridge will wait for the Max Response Delay before starting
to forward according to its MDB in order to let Membership Reports
enough time to be received and processed.

Currently, the test is waiting for exactly the default Max Response
Delay (10 seconds) which is racy and leads to failures [1].

Fix by reducing the Max Response Delay to 1 second.

[1]
 [...]
 # TEST: IPv4 host entries forwarding tests                            [FAIL]
 # Packet locally received after flood

Fixes: b6d00da08610 ("selftests: forwarding: Add bridge MDB test")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20240208155529.1199729-3-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>