Merge branch 'selftests-forwarding-various-improvements'

Ido Schimmel says:

====================
selftests: forwarding: Various improvements

This patchset speeds up the multipath tests (patches #1-#2) and makes
other tests more stable (patches #3-#6) so that they will not randomly
fail in the netdev CI.

On my system, after applying the first two patches, the run time of
gre_multipath_nh_res.sh is reduced by over 90%.
====================

Link: https://lore.kernel.org/r/20240304095612.462900-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>