No Router Advertisement packets on lowpan0 interface

[mkowalczyk88]

Default configuration of CI40 OpenWRT doesn't send RA packets on 6lowpan interface. This is a problem for 6lowpan clicker because the router address must be then explicitly configured on a clicker . If the sending of RA packets work properly, then there is no need of setting router address on a clicker and it can then use global addresses out-of-the-box.