[SQUASH ME] sixlowpan: use macro for iphc dispatch mask
ipv6: add some handy functions for ipv6_hdr_t
[SQUASH ME] sixlowpan.iphc_cbuf: Make iphc_cbuf thread safe
[SQUASH ME] sixlowpan.core: use sixlowpan_hc in core correctly
[SQUASH ME] sixlowpan.iphc: continue