i40e: adjust ITR max and min values

Set the ITR max and min values to match the hardware max value
and the recommended min value.  These values are shifted right
one bit because the register counts in 2 usec units, so leave
a comment to explain.

Change-ID: I289c27955cf6c566a6d21b95c3110b88cbb15dad
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.h

@@ -29,9 +29,8 @@
 
 /* Interrupt Throttling and Rate Limiting (storm control) Goodies */
 
-#define I40E_MAX_ITR               0x07FF
-#define I40E_MIN_ITR               0x0001
-#define I40E_ITR_USEC_RESOLUTION   2
+#define I40E_MAX_ITR               0x0FF0  /* reg uses 2 usec resolution */
+#define I40E_MIN_ITR               0x0004  /* reg uses 2 usec resolution */
 #define I40E_MAX_IRATE             0x03F
 #define I40E_MIN_IRATE             0x001
 #define I40E_IRATE_USEC_RESOLUTION 4