net: e1000e: solve insmod 'Unknown symbol mutex_lock' error

After I turn on the CONFIG_LOCK_STAT=y, insmod e1000e.ko will report:
[    5.641579] e1000e: Unknown symbol mutex_lock (err -2)
[   90.775705] e1000e: Unknown symbol mutex_lock (err -2)
[  132.252339] e1000e: Unknown symbol mutex_lock (err -2)

This problem fixed after include <linux/mutex.h>.
Signed-off-by: Hao Chen <chenhaoa@uniontech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -21,6 +21,7 @@
 #include <linux/ptp_classify.h>
 #include <linux/mii.h>
 #include <linux/mdio.h>
+#include <linux/mutex.h>
 #include <linux/pm_qos.h>
 #include "hw.h"