syscalls/sockioctl01: Cleanup first.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
syscalls/sockioctl01: Fixes.

* Use the tst_tmpdir() only once in global setup.

* Fix permission flags passed to mknod.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>