Logging: added feature for compact address logging (last 16 bits). Cleanup more logs in MAC layers, IPv6 and RPL

Simplify uip-ds6-nbr module further when NDP is disabled. Avoids known issue https://github.com/contiki-os/contiki/issues/1380 of neighbors in non-REACHABLE state.

This commit removes trailing spaces and converts
tabs to spaces in all files affected by fix-doxygen PR.

This commit fixes nearly all of the reported doxygen warnings.

I tried to not clutter the log with removed trailing spaces.
Removed whitespace and converted tab/spaces for all files affected by this commit
are in a separate branch.

* Make these blocks appear in the respective module pages
* Re-word \file blocks to bring them up to speed with what each file actually does nowadays

The reachable state might also be considered to keep the reachable
state since we are already not standard complaint. This reduces the
nbr discovery messages if nodes talk to each other periodically.

Followed by doxyen file and group tags.
This patch is only a first attempt to make provide a clean structure,
many more files require rework, too.

Moved the rimeaddr.[ch] code from the core/net/rime module to the core/net module, as it is used not only by rime code

Added the const keyword to IP address arguments that are not (and should not be) changed by the callee

1. Added #include header
2. Fixed #defines that weren't updated
3. Small change to comment that now points to correct RFC section

Moved ETX management from neighbor-info to rpl-of-etx. Avoids conversions between different fixed point representations, and simplifies neighbor management. Makes more clear how default-ETX and noack-ETX actually affect the rank. Removed neighbor-info and neighbor-attr.

Make DS6 neighbors use neighbor-table, and move all DS6 neighbor management from uip-ds6 to a new uip-ds6-neighbor module.