vlan-bridge-binding-sh flaky

Hi Ido!

tools/testing/selftests/net/vlan_bridge_binding.sh got flaky recently.

https://netdev.bots.linux.dev/contest.html?test=vlan-bridge-binding-sh

Is it due to Eric's change or something else? Used to be pretty solid. First lake a week ago and 8 more since, before that for 3 weeks there were 0 flakes.

The failure reason is the same across all the test runs: Observing an UP operational state instead of DOWN. I believe that's because link watch can delay carrier loss events by up to 1 second and that's the timeout the test is using.

I increased the timeout to 2 seconds and didn't observe a failure in over 100 iterations. Previously it failed after 48 iterations.

I will send a patch.