e1000e: add timeout for TX HW time stamping work

Hardware may fail to report time stamp e.g.:
 - when hardware time stamping is not enabled
 - when time stamp is requested shortly after ifup

Timeout time stamp reading work to prevent it from
scheduling itself indefinitely. Report timeout events
via system log and device stats.

Signed-off-by: Jakub Kicinski <kubakici@wp.pl>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/e1000.h

@@ -262,6 +262,7 @@ struct e1000_adapter {
 	u32 tx_head_addr;
 	u32 tx_fifo_size;
 	u32 tx_dma_failed;
+	u32 tx_hwtstamp_timeouts;
 
 	/* Rx */
 	bool (*clean_rx) (struct e1000_ring *ring, int *work_done,
@@ -334,6 +335,7 @@ struct e1000_adapter {
 	struct hwtstamp_config hwtstamp_config;
 	struct delayed_work systim_overflow_work;
 	struct sk_buff *tx_hwtstamp_skb;
+	unsigned long tx_hwtstamp_start;
 	struct work_struct tx_hwtstamp_work;
 	spinlock_t systim_lock;	/* protects SYSTIML/H regsters */
 	struct cyclecounter cc;