selftests: net/rds: add module not found

This fix solves this error, when calling kselftest with targets "net/rds":

The error was found by running tests manually with the command:
make kselftest TARGETS="net/rds"

The patch also specifies to import ip() function from the utils module.

Signed-off-by: Alessandro Zanni <alessandro.zanni87@gmail.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Link: https://patch.msgid.link/20241010194421.48198-1-alessandro.zanni87@gmail.com


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