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

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

It would be good to use the same mechanism for scheduling and dispatching
general net tests as the many forwarding tests already use. To that end,
move the logging helpers to net/lib.sh so that every net test can use them.

Existing lib.sh users might be using the name themselves. However lib.sh is
always sourced near the top of the file (checked), and whatever new
definition will simply override the one 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/a6fc083486493425b2c61185c327845b6ce3233a.1731589511.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>