net: dsa: bcm_sf2: Forcibly configure IMP port for 1Gb/sec

We are still experiencing some packet loss with the existing advanced
congestion buffering (ACB) settings with the IMP port configured for
2Gb/sec, so revert to conservative link speeds that do not produce
packet loss until this is resolved.

Fixes: 8f1880cbe8 ("net: dsa: bcm_sf2: Configure IMP port for 2Gb/sec")
Fixes: de34d7084e ("net: dsa: bcm_sf2: Only 7278 supports 2Gb/sec IMP port")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/bcm_sf2.c

@@ -69,8 +69,7 @@ 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);
-		if (priv->type == BCM7278_DEVICE_ID)
-			reg |= GMII_SPEED_UP_2G;
+		reg &= ~GMII_SPEED_UP_2G;
 		core_writel(priv, reg, offset);
 
 		/* Enable Broadcast, Multicast, Unicast forwarding to IMP port */