[PATCH v3] net: stmmac: Modify the judgment condition of "tx_avail" from 1 to 2

[Jakub Kicinski]

On Wed,  3 Dec 2025 09:31:52 +0800 2694439648 at qq.com wrote:
> -	if (unlikely(stmmac_tx_avail(priv, queue) <= (MAX_SKB_FRAGS + 1))) {
> +	if (unlikely(stmmac_tx_avail(priv, queue) <= (MAX_SKB_FRAGS + 2))) {

Please add a constant for "(MAX_SKB_FRAGS + 2)" and a comment next to
it explaining why the literal 2 is used.