igb: drop support for single buffer mode

This change removes support for single buffer mode from igb and makes the
driver function in packet split always.  The advantage to doing this is
that we can reduce total memory allocation overhead significantly as we
will only need to allocate one 1K slab per packet and then make use of a
reusable half page instead of allocating a 2K slab per packet.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by:  Aaron Brown  <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb.h

@@ -111,11 +111,9 @@ struct vf_data_storage {
 #define MAXIMUM_ETHERNET_VLAN_SIZE 1522
 
 /* Supported Rx Buffer Sizes */
-#define IGB_RXBUFFER_64    64     /* Used for packet split */
-#define IGB_RXBUFFER_128   128    /* Used for packet split */
-#define IGB_RXBUFFER_1024  1024
-#define IGB_RXBUFFER_2048  2048
+#define IGB_RXBUFFER_512   512
 #define IGB_RXBUFFER_16384 16384
+#define IGB_RX_HDR_LEN     IGB_RXBUFFER_512
 
 /* How many Tx Descriptors do we need to call netif_wake_queue ? */
 #define IGB_TX_QUEUE_WAKE	16
@@ -221,7 +219,6 @@ struct igb_ring {
 		struct {
 			struct igb_rx_queue_stats rx_stats;
 			struct u64_stats_sync rx_syncp;
-			u32 rx_buffer_len;
 		};
 	};
 };