enic: make vnic_wq_buf doubly linked

This patch makes vnic_wq_buf doubly liked list. This is needed for dma_mapping
error check, in case some frag's dma map fails, we need to move back and remove
previously queued buffers.
Signed-off-by: Govindarajulu Varadarajan <_govind@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cisco/enic/vnic_wq.c

@@ -47,11 +47,14 @@ static int vnic_wq_alloc_bufs(struct vnic_wq *wq)
 				wq->ring.desc_size * buf->index;
 			if (buf->index + 1 == count) {
 				buf->next = wq->bufs[0];
+				buf->next->prev = buf;
 				break;
 			} else if (j + 1 == VNIC_WQ_BUF_BLK_ENTRIES(count)) {
 				buf->next = wq->bufs[i + 1];
+				buf->next->prev = buf;
 			} else {
 				buf->next = buf + 1;
+				buf->next->prev = buf;
 				buf++;
 			}
 		}

drivers/net/ethernet/cisco/enic/vnic_wq.h

@@ -62,6 +62,7 @@ struct vnic_wq_buf {
 	uint8_t cq_entry; /* Gets completion event from hw */
 	uint8_t desc_skip_cnt; /* Num descs to occupy */
 	uint8_t compressed_send; /* Both hdr and payload in one desc */
+	struct vnic_wq_buf *prev;
 };
 
 /* Break the vnic_wq_buf allocations into blocks of 32/64 entries */