mac80211: fix ieee80211_change_mac() to use struct sockaddr

Setting the mac address from user space was buggy. For example, when
executing this command:

ip link set wlan0 address 00:1f:df:88:cd:55

mac80211 used the address 01:00:00:1f:df:88 instead. It was shifted two
bytes.

The reason was that the addr (type of void *) provided to
ieee80211_change_mac() is actually of type struct sockaddr, not just the
mac address array. Also the call to eth_mac_addr() expects the address to
be struct sockaddr.

Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>