BUG? flaky "migrate_reuseport/IPv4 TCP_NEW_SYN_RECV reqsk_timer_handler" test

[Martin KaFai Lau <martin.lau@linux.dev>]

Hi Kuniyuki,

The bpf CI has recently hit failure in the "migrate_reuseport/IPv4 
TCP_NEW_SYN_RECV" test. It does not always fail but becomes more flaky recently:
https://github.com/kernel-patches/bpf/actions/runs/8354884067/job/22869153115

It could be due to some slowness in the bpf CI environment but failing because 
of environment slowness is still not expected.

I took a very quick look. It seems like the test depends on the firing of the 
timer's handler "reqsk_timer_handler()", so there is a sleep(1) in the test.
May be the timer fired slower and the test failed? If that is the case, it may 
help to directly trace the reqsk_timer_handler() and wait for enough time to 
ensure it is called.

This test has been temporarily disabled for now 
(https://github.com/kernel-patches/vmtest/blob/master/ci/vmtest/configs/DENYLIST). 
Once you have a fix, we can re-enable it again to ensure this migrate feature 
will not regress.

Thanks,
Martin