Fix the wanxl firmware to include missing constants

Fix the wanxl firmware to include missing constants such as PARITY_NONE.  It
should be #including the linux/hdlc/ioctl.h header.

To make this work, we also have to guard parts of ioctl.h with !__ASSEMBLY__.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>