net: stmmac: xgmac: Only get SPH header len if available

Split Header length is only available when L34T == 0. Fix this by
correctly checking if L34T is zero before trying to get Header length.

Fixes: 67afd6d1 ("net: stmmac: Add Split Header support and enable it in XGMAC cores")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c

@@ -288,7 +288,8 @@ static int dwxgmac2_get_rx_hash(struct dma_desc *p, u32 *hash,
 
 static int dwxgmac2_get_rx_header_len(struct dma_desc *p, unsigned int *len)
 {
-	*len = le32_to_cpu(p->des2) & XGMAC_RDES2_HL;
+	if (le32_to_cpu(p->des3) & XGMAC_RDES3_L34T)
+		*len = le32_to_cpu(p->des2) & XGMAC_RDES2_HL;
 	return 0;
 }