net: dsa: b53: Force flow control for BCM5301X CPU port(s)

Just like what b53_adjust_link() does, force flow control for the
BCM5301X CPU port(s) by forcing rx_pause and tx_pause in
b53_phylink_mac_link_up(). Preparatory step for getting rid of
b53_adjust_link().

Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20240423183339.1368511-5-florian.fainelli@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/b53/b53_common.c

@@ -1475,6 +1475,10 @@ static void b53_phylink_mac_link_up(struct dsa_switch *ds, int port,
 		return;
 
 	if (mode == MLO_AN_FIXED) {
+		/* Force flow control on BCM5301x's CPU port */
+		if (is5301x(dev) && dsa_is_cpu_port(ds, port))
+			tx_pause = rx_pause = true;
+
 		b53_force_port_config(dev, port, speed, duplex,
 				      tx_pause, rx_pause);
 		b53_force_link(dev, port, true);