Ensure correct endianness for pprzlink

[podhrmic]

Based on my talk with @gautierhattenberger

pprzlink uses the host byte order, which is typically little endian for most autopilots. Conveniently, most computers are little-endian these days, so it works out. However, it would be good to ensure that the byte order is the same for both parties, or even better switch to network byte order for pprzlink to make this universal.

Possible solution: add hton*()/ntoh*() shims to the generated code.

I might get to this later in the year, hence assigning to myself.