USB: usbdevfs: sanitize flags more

Requesting a ZERO_PACKET or not is sensible only for output.
In the input direction the device decides.
Likewise accepting short packets makes sense only for input.

This allows operation with panic_on_warn without opening up
a local DOS.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Reported-by:  <syzbot+843efa30c8821bd69f53@syzkaller.appspotmail.com>
Fixes: 0cb54a3e

 ("USB: debugging code shouldn't alter control flow")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>