igbvf: Change IGBVF_MIN to allow set rx/tx value between 64 and 80

Change the minimum value of RX/TX descriptors to 64 to enable setting the rx/tx
value between 64 and 80. All igbvf devices can use as low as 64 descriptors.
This change will unify igbvf with other drivers.
Based on commit 7b1be198 ("e1000e: lower ring minimum size to 64")

Fixes: d4e0fe01 ("igbvf: add new driver to support 82576 virtual functions")
Signed-off-by: Olga Zaborska <olga.zaborska@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igbvf/igbvf.h

@@ -39,11 +39,11 @@ enum latency_range {
 /* Tx/Rx descriptor defines */
 #define IGBVF_DEFAULT_TXD	256
 #define IGBVF_MAX_TXD		4096
-#define IGBVF_MIN_TXD		80
+#define IGBVF_MIN_TXD		64
 
 #define IGBVF_DEFAULT_RXD	256
 #define IGBVF_MAX_RXD		4096
-#define IGBVF_MIN_RXD		80
+#define IGBVF_MIN_RXD		64
 
 #define IGBVF_MIN_ITR_USECS	10 /* 100000 irq/sec */
 #define IGBVF_MAX_ITR_USECS	10000 /* 100    irq/sec */