bonding: fix ad_actor_system option setting to default

When 802.3ad bond mode is configured the ad_actor_system option is set to
"00:00:00:00:00:00". But when trying to set the all-zeroes MAC as actors'
system address it was failing with EINVAL.

An all-zeroes ethernet address is valid, only multicast addresses are not
valid values.

Fixes: 171a42c3 ("bonding: add netlink support for sys prio, actor sys mac, and port key")
Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Link: https://lore.kernel.org/r/20211221111345.2462-1-ffmancera@riseup.netSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/bonding.rst

@@ -196,11 +196,12 @@ ad_actor_sys_prio
 ad_actor_system
 
 	In an AD system, this specifies the mac-address for the actor in
-	protocol packet exchanges (LACPDUs). The value cannot be NULL or
-	multicast. It is preferred to have the local-admin bit set for this
-	mac but driver does not enforce it. If the value is not given then
-	system defaults to using the masters' mac address as actors' system
-	address.
+	protocol packet exchanges (LACPDUs). The value cannot be a multicast
+	address. If the all-zeroes MAC is specified, bonding will internally
+	use the MAC of the bond itself. It is preferred to have the
+	local-admin bit set for this mac but driver does not enforce it. If
+	the value is not given then system defaults to using the masters'
+	mac address as actors' system address.
 
 	This parameter has effect only in 802.3ad mode and is available through
 	SysFs interface.

drivers/net/bonding/bond_options.c

@@ -1526,7 +1526,7 @@ static int bond_option_ad_actor_system_set(struct bonding *bond,
 		mac = (u8 *)&newval->value;
 	}
 
-	if (!is_valid_ether_addr(mac))
+	if (is_multicast_ether_addr(mac))
 		goto err;
 
 	netdev_dbg(bond->dev, "Setting ad_actor_system to %pM\n", mac);