nfp: fix free list buffer size reporting

XDP headroom should not be included in free list buffer size.

Fixes: 6fe0c3b4 ("nfp: add support for xdp_adjust_head()")
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfp_net_common.c

@@ -2165,7 +2165,7 @@ nfp_net_tx_ring_hw_cfg_write(struct nfp_net *nn,
  */
 static int nfp_net_set_config_and_enable(struct nfp_net *nn)
 {
-	u32 new_ctrl, update = 0;
+	u32 bufsz, new_ctrl, update = 0;
 	unsigned int r;
 	int err;
 
@@ -2199,8 +2199,9 @@ static int nfp_net_set_config_and_enable(struct nfp_net *nn)
 	nfp_net_write_mac_addr(nn);
 
 	nn_writel(nn, NFP_NET_CFG_MTU, nn->dp.netdev->mtu);
-	nn_writel(nn, NFP_NET_CFG_FLBUFSZ,
-		  nn->dp.fl_bufsz - NFP_NET_RX_BUF_NON_DATA);
+
+	bufsz = nn->dp.fl_bufsz - nn->dp.rx_dma_off - NFP_NET_RX_BUF_NON_DATA;
+	nn_writel(nn, NFP_NET_CFG_FLBUFSZ, bufsz);
 
 	/* Enable device */
 	new_ctrl |= NFP_NET_CFG_CTRL_ENABLE;