aquantia: Remove the build_skb path

When performing IPv6 forwarding, there is an expectation that SKBs
will have some headroom. When forwarding a packet from the aquantia
driver, this does not always happen, triggering a kernel warning.

aq_ring.c has this code (edited slightly for brevity):

if (buff->is_eop && buff->len <= AQ_CFG_RX_FRAME_MAX - AQ_SKB_ALIGN) {
    skb = build_skb(aq_buf_vaddr(&buff->rxdata), AQ_CFG_RX_FRAME_MAX);
} else {
    skb = napi_alloc_skb(napi, AQ_CFG_RX_HDR_SIZE);

There is a significant difference between the SKB produced by these
2 code paths. When napi_alloc_skb creates an SKB, there is a certain
amount of headroom reserved. However, this is not done in the
build_skb codepath.

As the hardware buffer that build_skb is built around does not
handle the presence of the SKB header, this code path is being
removed and the napi_alloc_skb path will always be used. This code
path does have to copy the packet header into the SKB, but it adds
the packet data as a frag.

Fixes: 018423e9 ("net: ethernet: aquantia: Add ring support code")
Signed-off-by: Lincoln Ramsay <lincoln.ramsay@opengear.com>
Link: https://lore.kernel.org/r/MWHPR1001MB23184F3EAFA413E0D1910EC9E8FC0@MWHPR1001MB2318.namprd10.prod.outlook.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/aquantia/atlantic/aq_ring.c

@@ -413,26 +413,6 @@ int aq_ring_rx_clean(struct aq_ring_s *self,
 					      buff->rxdata.pg_off,
 					      buff->len, DMA_FROM_DEVICE);
 
-		/* for single fragment packets use build_skb() */
-		if (buff->is_eop &&
-		    buff->len <= AQ_CFG_RX_FRAME_MAX - AQ_SKB_ALIGN) {
-			skb = build_skb(aq_buf_vaddr(&buff->rxdata),
-					AQ_CFG_RX_FRAME_MAX);
-			if (unlikely(!skb)) {
-				u64_stats_update_begin(&self->stats.rx.syncp);
-				self->stats.rx.skb_alloc_fails++;
-				u64_stats_update_end(&self->stats.rx.syncp);
-				err = -ENOMEM;
-				goto err_exit;
-			}
-			if (is_ptp_ring)
-				buff->len -=
-					aq_ptp_extract_ts(self->aq_nic, skb,
-						aq_buf_vaddr(&buff->rxdata),
-						buff->len);
-			skb_put(skb, buff->len);
-			page_ref_inc(buff->rxdata.page);
-		} else {
 		skb = napi_alloc_skb(napi, AQ_CFG_RX_HDR_SIZE);
 		if (unlikely(!skb)) {
 			u64_stats_update_begin(&self->stats.rx.syncp);
@@ -468,11 +448,10 @@ int aq_ring_rx_clean(struct aq_ring_s *self,
 			buff_ = buff;
 			i = 1U;
 			do {
-					next_ = buff_->next,
+				next_ = buff_->next;
 				buff_ = &self->buff_ring[next_];
 
-					dma_sync_single_range_for_cpu(
-							aq_nic_get_dev(self->aq_nic),
+				dma_sync_single_range_for_cpu(aq_nic_get_dev(self->aq_nic),
 							      buff_->rxdata.daddr,
 							      buff_->rxdata.pg_off,
 							      buff_->len,
@@ -492,7 +471,6 @@ int aq_ring_rx_clean(struct aq_ring_s *self,
 
 			} while (!buff_->is_eop);
 		}
-		}
 
 		if (buff->is_vlan)
 			__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q),