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>