[VLAN]: Lost rtnl_unlock() in vlan_ioctl()

The SET_VLAN_NAME_TYPE_CMD command w/o CAP_NET_ADMIN capability
doesn't release the rtnl lock.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>