mac80211: use unaligned safe memcmp() in-place of compare_ether_addr()

After fixing zd1211rw: use unaligned safe memcmp() in-place of
compare_ether_addr(), I started to see kernel log messages detailing
unaligned access:

  Kernel unaligned access at TPC[100f7f44] sta_info_get+0x24/0x68 [mac80211]

As with the aforementioned patch, the unaligned access was eminating
from a compare_ether_addr() call. Concerned that whilst it was safe to
assume that unalignment was the norm for the zd1211rw, and take
preventative measures, it may not be the case or acceptable to use the
easy fix of changing the call to memcmp().

My research however indicated that it was OK to do this, as there are
a few instances where memcmp() is the preferred mechanism for doing
mac address comparisons throughout the module.

Signed-off-by: Shaddy Baddah <shaddy_baddah@hotmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>