sfc: Replace stats_enabled flag with a disable count

Currently we use a spin-lock to serialise statistics fetches and also
to inhibit them for short periods of time, plus a flag to
enable/disable statistics fetches for longer periods of time, during
online reset.  This was apparently insufficient to deal with the several
reasons for stats being disabled.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/sfc/net_driver.h b/drivers/net/sfc/net_driver.h
index 8eb411a..e019ad1 100644
--- a/drivers/net/sfc/net_driver.h
+++ b/drivers/net/sfc/net_driver.h
@@ -754,8 +754,7 @@
  *	&struct net_device_stats.
  * @stats_buffer: DMA buffer for statistics
  * @stats_lock: Statistics update lock. Serialises statistics fetches
- * @stats_enabled: Temporarily disable statistics fetches.
- *	Serialised by @stats_lock
+ * @stats_disable_count: Nest count for disabling statistics fetches
  * @mac_op: MAC interface
  * @mac_address: Permanent MAC address
  * @phy_type: PHY type
@@ -837,7 +836,7 @@
 	struct efx_mac_stats mac_stats;
 	struct efx_buffer stats_buffer;
 	spinlock_t stats_lock;
-	bool stats_enabled;
+	unsigned int stats_disable_count;
 
 	struct efx_mac_operations *mac_op;
 	unsigned char mac_address[ETH_ALEN];