net: stmmac: Fix TSO descriptor with Enhanced Addressing

When using addressing > 32 bits the TSO first descriptor only has the
header so we can't set the payload field for this descriptor. Let's
reset the variable so that buffer 2 value is zero.

Fixes: a993db88 ("net: stmmac: Enable support for > 32 Bits addressing in XGMAC")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -2996,6 +2996,7 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 		stmmac_set_desc_addr(priv, first, des);
 		tmp_pay_len = pay_len;
 		des += proto_hdr_len;
+		pay_len = 0;
 	}
 
 	stmmac_tso_allocator(priv, des, tmp_pay_len, (nfrags == 0), queue);