[TEST] conntrack_reverse_clash.sh flakes

[Jakub Kicinski <kuba@kernel.org>]

Hi Florian!

We have a new faster NIPA setup, and now on non-debug builds we see 
a few (4 a week to be exact) flakes in conntrack_reverse_clash.sh

List of flakes from the last 100 runs:
https://netdev.bots.linux.dev/contest.html?pass=0&test=conntrack-reverse-clash-sh

Example:

# selftests: net/netfilter: conntrack_reverse_clash.sh
# Port number changed, wanted 56789 got 5950
# ERROR: SNAT performed without any matching snat rule
# kill: sending signal to 16051 failed: No such process
not ok 1 selftests: net/netfilter: conntrack_reverse_clash.sh # exit=1

Looks like the test also occasionally flaked on the old setup ("remote"
column with "metal" instead of "virt") which is now shut down:

# selftests: net/netfilter: conntrack_reverse_clash.sh
# Port number changed, wanted 56789 got 54630
# Port number changed, wanted 56790 got 25814
# ERROR: SNAT performed without any matching snat rule
not ok 1 selftests: net/netfilter: conntrack_reverse_clash.sh # exit=1

so this isn't new, just more likely now..

Could you TAL when you have spare cycles? (BTW the new setup is owned 
by netdev foundation so I can give you access if that helps).