ipw2x00: slight optimization of addr compare

Use possibly more efficient ether_addr_equal
instead of memcmp.

Cc: Stanislav Yakovlev <stas.yakovlev@gmail.com>
Cc: John W. Linville <linville@tuxdriver.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>