selftests: net: lib: Move logging from forwarding/lib.sh here

Many net selftests invent their own logging helpers. These really should be
in a library sourced by these tests. Currently forwarding/lib.sh has a
suite of perfectly fine logging helpers, but sourcing a forwarding/ library
from a higher-level directory smells of layering violation. In this patch,
move the logging helpers to net/lib.sh so that every net test can use them.

Together with the logging helpers, it's also necessary to move
pause_on_fail(), and EXIT_STATUS and RET.

Existing lib.sh users might be using these same names for their functions
or variables. However lib.sh is always sourced near the top of the
file (checked), and whatever new definitions will simply override the ones
provided by lib.sh.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://patch.msgid.link/edd3785a3bd72ffbe1409300989e993ee50ae98b.1731589511.git.petrm@nvidia.com


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