p54: move statistic timer update routine into a workqueue

This patch moves a good chunk of code from the former statistic update
timer routine into a workqueue, which is kindly provided by mac80211.

Also as a nice side-effect we can lay the foundation for other
essential housekeeping features we want to do in the future.
e.g:
 - drain the (clogged) tx_queue.
 - initiate bursts.

Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/p54/p54common.h b/drivers/net/wireless/p54/p54common.h
index 5a68fda..06e1643 100644
--- a/drivers/net/wireless/p54/p54common.h
+++ b/drivers/net/wireless/p54/p54common.h
@@ -355,6 +355,11 @@
 	u8 align[0];
 } __attribute__ ((packed));
 
+/* unit is ms */
+#define P54_TX_FRAME_LIFETIME 2000
+#define P54_TX_TIMEOUT 4000
+#define P54_STATISTICS_UPDATE 5000
+
 #define P54_FILTER_TYPE_NONE		0
 #define P54_FILTER_TYPE_STATION		BIT(0)
 #define P54_FILTER_TYPE_IBSS		BIT(1)