Merge branch 'selftests-pmtu-sh-fix-cleanup-of-processes-launched-in-subshell'

Merge branch 'selftests-pmtu-sh-fix-cleanup-of-processes-launched-in-subshell'

Guillaume Nault says:

====================
selftests: pmtu.sh: Fix cleanup of processes launched in subshell.

Depending on the options used, pmtu.sh may launch tcpdump and nettest
processes in the background. However it fails to clean them up after
the tests complete.

Patch 1 allows the cleanup() function to read the list of PIDs launched
by the tests.
Patch 2 fixes the way the nettest PIDs are retrieved.
====================

Link: https://lore.kernel.org/r/cover.1646776561.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>