net: dsa: bcm_sf2: use 2 Gbps IMP port link on BCM4908

BCM4908 uses 2 Gbps link between switch and the Ethernet interface.
Without this BCM4908 devices were able to achieve only 2 x ~895 Mb/s.
This allows handling e.g. NAT traffic with 940 Mb/s.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/bcm_sf2.c

@@ -114,7 +114,10 @@ static void bcm_sf2_imp_setup(struct dsa_switch *ds, int port)
 		/* Force link status for IMP port */
 		reg = core_readl(priv, offset);
 		reg |= (MII_SW_OR | LINK_STS);
-		reg &= ~GMII_SPEED_UP_2G;
+		if (priv->type == BCM4908_DEVICE_ID)
+			reg |= GMII_SPEED_UP_2G;
+		else
+			reg &= ~GMII_SPEED_UP_2G;
 		core_writel(priv, reg, offset);
 
 		/* Enable Broadcast, Multicast, Unicast forwarding to IMP port */