test_sysctl: fix sysctl.sh by making it executable

We had just forogtten to do this. Without this the following test fails:

$ sudo make -C tools/testing/selftests/sysctl/ run_tests
make: Entering directory '/home/mcgrof/linux-next/tools/testing/selftests/sysctl'
/bin/sh: ./sysctl.sh: Permission denied
selftests:  sysctl.sh [FAIL]
/home/mcgrof/linux-next/tools/testing/selftests/sysctl
make: Leaving directory '/home/mcgrof/linux-next/tools/testing/selftests/sysctl'

Fixes: 64b67120 ("test_sysctl: add generic script to expand on tests")
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>