pktbuf: optimize size overhead in packet buffer
Merge pull request #1959 from authmillenon/pktbuf-opt

pktbuf: optimize size overhead in packet buffer
unittests: Add missing semicolons to macro calls
make: remove downloader "axel"

Breaks for `make -B`. If the file already exists, then `axel` fails
because it does not find the status file for the download.
Merge pull request #1929 from Kijewski/no-axel

make: remove downloader "axel"
Merge pull request #1972 from authmillenon/unittests-semicolons

unittests: Add missing semicolons to macro calls
embunit: fix macros
Fix stuff