ixgbe: fix possible divide by zero in ixgbe_update_itr

Protect the code by bailing out of ixgbe_update_itr() when this occurs.
The next call to ixgbe_update_itr will continue to dynamically update ITR.
Signed-of-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -2095,6 +2095,9 @@ static void ixgbe_update_itr(struct ixgbe_q_vector *q_vector,
 	 */
 	/* what was last interrupt timeslice? */
 	timepassed_us = q_vector->itr >> 2;
+	if (timepassed_us == 0)
+		return;
+
 	bytes_perint = bytes / timepassed_us; /* bytes/usec */
 
 	switch (itr_setting) {