switchdev: fix: erasing too much of vlan obj when handling multiple vlan specs

When adding vlans with multiple IFLA_BRIDGE_VLAN_INFO attrs set in AFSPEC,
we would wipe the vlan obj struct after the first IFLA_BRIDGE_VLAN_INFO.
Fix this by only clearing what's necessary on each IFLA_BRIDGE_VLAN_INFO
iteration.

Fixes: 9e8f4a54 ("switchdev: push object ID back to object structure")
Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/switchdev/switchdev.c

@@ -869,7 +869,7 @@ static int switchdev_port_br_afspec(struct net_device *dev,
 			err = f(dev, &vlan.obj);
 			if (err)
 				return err;
-			memset(&vlan, 0, sizeof(vlan));
+			vlan.vid_begin = 0;
 		} else {
 			if (vlan.vid_begin)
 				return -EINVAL;
@@ -878,7 +878,7 @@ static int switchdev_port_br_afspec(struct net_device *dev,
 			err = f(dev, &vlan.obj);
 			if (err)
 				return err;
-			memset(&vlan, 0, sizeof(vlan));
+			vlan.vid_begin = 0;
 		}
 	}