Tracking issue for RPL

[thvdveld]

I create this tracking issue for the RPL support (instead of 1 big PR #627) RFC6550.

• Add wire representation for the RPL protocol. #766
• IPv6 Extension Headers rewrite #781 replacing
  • 6LoWPAN Hop-by-Hop Header compression #765
  • 6LoWPAN Routing Header compression #770
• RPL Hop-by-Hop option #767
• Implement the sequence counter from RFC6550 7.2 #772
• Implementation of the Trickle algorithm defined in RFC6206 #773
• Implement RPL Rank logic #777
• Add RPL relations table #790
• RPL: add objective function and parent set #798 (Objective Function Zero RFC6552 and preferred parent set)
• Add 6LoWPAN extension header compression and decompression #829 (for RPL Hop-by-hop and source routing header support)
• Mode of operation 0: no downward routes maintained
• Mode of operation 1: upward routes, without storing mode
• Mode of operation 2: upward routes, with storing (without broadcast)
• Mode of operation 3: upward routes, with storing (with broadcast)