Optimizations

Trickle timer implementation

The Trickle timer that is implemented in smoltcp uses the enhanced Trickle timer.

Note that Contiki-NG also implements this timer.

Rank-Error

The standard sais that the rank-error bit must be set when a Rank error is detected. A rank error occurs when a packet is traveling throught the DODAG in the wrong direction. Such an error is not considered critical, but a second occurence is. The standard provides an example in which case it might occur. However, this looks like an edge case that will never occur. Therefor, we immediatly drop a packet when a rank error is detected.