mac820154: don't set monitor dev_addr

This patch removes the setting of dev_addr on a monitor device. This
address should be zero. A monitor should only sniff and send raw frames
out. The address should be never used by upper layers and receiving
frame parsing.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>