net: stmmac: Enable 16KB buffer size

BugLink: https://bugs.launchpad.net/bugs/1860681

commit b2f3a481 upstream.

XGMAC supports maximum MTU that can go to 16KB. Lets add this check in
the calculation of RX buffer size.

Fixes: 7ac6653a ("stmmac: Move the STMicroelectronics driver")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

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

@@ -935,7 +935,9 @@ static int stmmac_set_bfsize(int mtu, int bufsize)
 {
 	int ret = bufsize;
 
-	if (mtu >= BUF_SIZE_4KiB)
+	if (mtu >= BUF_SIZE_8KiB)
+		ret = BUF_SIZE_16KiB;
+	else if (mtu >= BUF_SIZE_4KiB)
 		ret = BUF_SIZE_8KiB;
 	else if (mtu >= BUF_SIZE_2KiB)
 		ret = BUF_SIZE_4KiB;