[SQUASH ME] fix test framework
[SQUASH ME] reduce scope of api_res
core: Fix msg_send_receive

Fixes #1935
[SQUASH ME] sixlowpan.core: silence valgrind
[SQUASH ME] sixlowpan.hc.tests: fix wrong dest size
[SQUASH ME] sixlowpan.hc: use byteorder.h for new datatypes
[SQUASH ME] sixlowpan.hc: reduce scope of prev
[SQUASH ME] sixlowpan.hc: move possible NULL pointer derefentiation
[SQUASH ME] sixlowpan: define possibly missing errno
[SQUASH ME] sixlowpan.hc: statically initialize dispatch array for decoding
[SQUASH ME] sixlowpan.hc.tests: silence type-punned casting warnings