iwlwifi: pcie: fix support for transmitting SKBs with fraglist

When the implementation of SKBs with fraglist was sent upstream, a
merge-damage occurred and half the patch was not applied.

This causes problems in high-throughput situations with AX200 devices,
including low throughput and FW crashes.

Introduce the part that was missing from the original patch.

Fixes: 0044f171 ("iwlwifi: pcie: support transmitting SKBs with fraglist")
Cc: stable@vger.kernel.org # 4.20+
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
[ This patch was created by me, but the original author of this code
  is Johannes, so his s-o-b is here and he's marked as the author of
  the patch. ]
Signed-off-by: NLuca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/tx-gen2.c

@@ -468,6 +468,7 @@ iwl_tfh_tfd *iwl_pcie_gen2_build_tx(struct iwl_trans *trans,
 	dma_addr_t tb_phys;
 	int len, tb1_len, tb2_len;
 	void *tb1_addr;
+	struct sk_buff *frag;
 
 	tb_phys = iwl_pcie_get_first_tb_dma(txq, idx);
 
@@ -516,6 +517,19 @@ iwl_tfh_tfd *iwl_pcie_gen2_build_tx(struct iwl_trans *trans,
 	if (iwl_pcie_gen2_tx_add_frags(trans, skb, tfd, out_meta))
 		goto out_err;
 
+	skb_walk_frags(skb, frag) {
+		tb_phys = dma_map_single(trans->dev, frag->data,
+					 skb_headlen(frag), DMA_TO_DEVICE);
+		if (unlikely(dma_mapping_error(trans->dev, tb_phys)))
+			goto out_err;
+		iwl_pcie_gen2_set_tb(trans, tfd, tb_phys, skb_headlen(frag));
+		trace_iwlwifi_dev_tx_tb(trans->dev, skb,
+					frag->data,
+					skb_headlen(frag));
+		if (iwl_pcie_gen2_tx_add_frags(trans, frag, tfd, out_meta))
+			goto out_err;
+	}
+
 	return tfd;
 
 out_err: