selftests: forwarding: Fix bridge locked port test flakiness

The redirection test case fails in the netdev CI on debug kernels
because an FDB entry is learned despite the presence of a tc filter that
redirects incoming traffic [1].

I am unable to reproduce the failure locally, but I can see how it can
happen given that learning is first enabled and only then the ingress tc
filter is configured. On debug kernels the time window between these two
operations is longer compared to regular kernels, allowing random
packets to be transmitted and trigger learning.

Fix by reversing the order and configure the ingress tc filter before
enabling learning.

[1]
[...]
 # TEST: Locked port MAB redirect                                      [FAIL]
 # Locked entry created for redirected traffic

Fixes: 38c43a1c ("selftests: forwarding: Add test case for traffic redirection from a locked port")
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/20240208155529.1199729-5-idosch@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>