selftests: ncdevmem: Properly reset flow steering

ntuple off/on might be not enough to do it on all NICs.
Add a bunch of shell crap to explicitly remove the rules.

Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20241107181211.3934153-8-sdf@fomichev.me


Signed-off-by: Jakub Kicinski <kuba@kernel.org>