selftests: net: rds: add include.sh to EXTRA_CLEAN

The include.sh file is generated when building the net/rds selftests,
but there is no rule to delete it with the clean target. Add the file to
EXTRA_CLEAN in order to remove it when required.

Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241005-net-selftests-gitignore-v2-2-3a0b2876394a@gmail.com


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