selftests: net: rds: add gitignore file for include.sh

The generated include.sh should be ignored by git. Create a new
gitignore and add the file to the list.
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-v2-3-3a0b2876394a@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/rds/.gitignore

+include.sh