remove vtimer object before (re)scheduling it
always append include pathes
use local packet_length variable in sendto

Having a global packet_length variable doesn't seem to be the best
idea. To avoid trouble, a scope local variable should be preferred.
SAFEST specific output
printf is used in sixlowpan mac layer, stack needs to be adjusted
initializes RPL instances
debug output when joining a dodag
set received parent lifetime when creating a new parent