When UIP_ND6_SEND_NS is enabled, I've noticed that unreachable
neighbours still remains in REACHABLE state even if lifetime
(nbr->reachable) expired.
During network init 'tcpip_process' is scheduling
'uip_ds6_timer_periodic' is to tick every 100ms and make necessary
expirations.
When MAC addres is received from slip-radio (from 'etimer_process'
context), network is "reinitialized" and timer 'uip_ds6_timer_periodic'
is set again with wrong process.
Some calls to `rpl_set_root` select a hardcoded DODAG ID
(0x1111, 0x1100, 0, 0, 0, 0, 0, 0x0011)
This is against what RFC 6550 says. We change these calls
to select a DODAG ID corresponding to a routable v6 address
corresponding to the root
