selftests: net: Add on/off checks for non-fixed features of interface

Implement on/off testing for all non-fixed features via while loop.

Signed-off-by: Abhinav Jain <jain.abhinav177@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240821171903.118324-3-jain.abhinav177@gmail.com


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