ixgbevf: Add lock around mailbox ops to prevent simultaneous access

This change adds a spinlock around the mailbox accesses to prevent
simultaneous access to the mailboxes.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h b/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h
index e167d1b..66858b5 100644
--- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h
+++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h
@@ -249,6 +249,8 @@
 	bool link_up;
 
 	struct work_struct watchdog_task;
+
+	spinlock_t mbx_lock;
 };
 
 enum ixbgevf_state_t {