net: bridge: fix error in br_multicast_add_port when CONFIG_NET_SWITCHDEV=n

When CONFIG_NET_SWITCHDEV is disabled, the shim for switchdev_port_attr_set
inside br_mc_disabled_update returns -EOPNOTSUPP. This is not caught,
and propagated to the caller of br_multicast_add_port, preventing ports
from joining the bridge.

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Fixes: ae1ea84b

 ("net: bridge: propagate error code and extack from br_mc_disabled_update")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>