6lowpan: check tc compression only on dscp
6lowpan: create macros to check on dscp and flow lbl
6lowpan: add function set_hc_ptr_data
6lowpan: introduce function lowpan_fetch_skb
6lowpan: zero ipv6hdr struct
6lowpan: rework tc and flbl compression.
6lowpan: setting LOWPAN_MAX_HEADER_LENGTH