net: dsa: vsc73xx: fix port MAC configuration in full duplex mode

According to the datasheet description ("Port Mode Procedure" in 5.6.2),
the VSC73XX_MAC_CFG_WEXC_DIS bit is configured only for half duplex mode.

The WEXC_DIS bit is responsible for MAC behavior after an excessive
collision. Let's set it as described in the datasheet.

Fixes: 05bd97fc ("net: dsa: Add Vitesse VSC73xx DSA router driver")
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/vitesse-vsc73xx-core.c

@@ -957,6 +957,11 @@ static void vsc73xx_mac_link_up(struct phylink_config *config,
 
 	if (duplex == DUPLEX_FULL)
 		val |= VSC73XX_MAC_CFG_FDX;
+	else
+		/* In datasheet description ("Port Mode Procedure" in 5.6.2)
+		 * this bit is configured only for half duplex.
+		 */
+		val |= VSC73XX_MAC_CFG_WEXC_DIS;
 
 	/* This routine is described in the datasheet (below ARBDISC register
 	 * description)
@@ -967,7 +972,6 @@ static void vsc73xx_mac_link_up(struct phylink_config *config,
 	get_random_bytes(&seed, 1);
 	val |= seed << VSC73XX_MAC_CFG_SEED_OFFSET;
 	val |= VSC73XX_MAC_CFG_SEED_LOAD;
-	val |= VSC73XX_MAC_CFG_WEXC_DIS;
 
 	/* Those bits are responsible for MTU only. Kernel takes care about MTU,
 	 * let's enable +8 bytes frame length unconditionally.