wireless: Use eth_<foo>_addr instead of memset

Use the built-in function instead of memset.

Miscellanea:

Add #include <linux/etherdevice.h> where appropriate
Use ETH_ALEN instead of 6

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>