Rename mavlink to radio_link

- split link state from slip structures and encapsulate it completely
- allocate interface specific buffers on demand
added initial work on network coding.

Refactor network coding
Simplify test result handling
Add window size to ACK, ensure only one new degree of freedom per packet
Reduce seq to a rotating uint8
Build network_coding.c into servald, use more constants instead of magic numbers
Initial implementation of network coding over RFD900
Dont resend packets over a 'reliable' link
Increase default mdp timeout & make it configurable
Add network coding stats to html output
Encapsulate rhizome fetch logging
Drop radio packets based on the probability of receiving the header
Reject packets with a jump in sequence numbers
Use interval parameter correctly even for unlimited pings
Remember the time that each packet was added
Tweak radio link to reduce peak latency
Increase mdp timeout based on file size
Fix typo
Simplify handling of mdp client address
Add support sending and receiving packets in new api