bnxt_en: Fix and simplify XDP transmit path

Fix the missing length hint in the TX BD for the XDP transmit path.  The
length hint is required on legacy chips.

Also, simplify the code by eliminating the first_buf local variable.
tx_buf contains the same value.  The opaque value only needs to be set
on the first BD.  Fix this also for correctness.

Fixes: a7559bc8c1 ("bnxt: support transmit and free of aggregation buffers")
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c

@@ -28,7 +28,7 @@ struct bnxt_sw_tx_bd *bnxt_xmit_bd(struct bnxt *bp,
 				   struct xdp_buff *xdp)
 {
 	struct skb_shared_info *sinfo;
-	struct bnxt_sw_tx_bd *tx_buf, *first_buf;
+	struct bnxt_sw_tx_bd *tx_buf;
 	struct tx_bd *txbd;
 	int num_frags = 0;
 	u32 flags;
@@ -43,13 +43,14 @@ struct bnxt_sw_tx_bd *bnxt_xmit_bd(struct bnxt *bp,
 	/* fill up the first buffer */
 	prod = txr->tx_prod;
 	tx_buf = &txr->tx_buf_ring[prod];
-	first_buf = tx_buf;
 	tx_buf->nr_frags = num_frags;
 	if (xdp)
 		tx_buf->page = virt_to_head_page(xdp->data);
 
 	txbd = &txr->tx_desc_ring[TX_RING(prod)][TX_IDX(prod)];
-	flags = ((len) << TX_BD_LEN_SHIFT) | ((num_frags + 1) << TX_BD_FLAGS_BD_CNT_SHIFT);
+	flags = (len << TX_BD_LEN_SHIFT) |
+		((num_frags + 1) << TX_BD_FLAGS_BD_CNT_SHIFT) |
+		bnxt_lhint_arr[len >> 9];
 	txbd->tx_bd_len_flags_type = cpu_to_le32(flags);
 	txbd->tx_bd_opaque = prod;
 	txbd->tx_bd_haddr = cpu_to_le64(mapping);
@@ -82,7 +83,6 @@ struct bnxt_sw_tx_bd *bnxt_xmit_bd(struct bnxt *bp,
 
 		flags = frag_len << TX_BD_LEN_SHIFT;
 		txbd->tx_bd_len_flags_type = cpu_to_le32(flags);
-		txbd->tx_bd_opaque = prod;
 		txbd->tx_bd_haddr = cpu_to_le64(frag_mapping);
 
 		len = frag_len;
@@ -96,7 +96,7 @@ struct bnxt_sw_tx_bd *bnxt_xmit_bd(struct bnxt *bp,
 	prod = NEXT_TX(prod);
 	txr->tx_prod = prod;
 
-	return first_buf;
+	return tx_buf;
 }
 
 static void __bnxt_xmit_xdp(struct bnxt *bp, struct bnxt_tx_ring_info *txr,