While reviewing #9942 I noticed that the documentation on the netdev
driver API is unclear and in some cases outright contradicting itself:
> ```
> @return number of bytes used from @p value
> @return `< 0` on error, 0 on success
> ```
IMHO this is unacceptable for such a central API where communication
This fixes a few things and also clarifies preconditions:
- Specifies negative `errno`s clearly so all drivers return the same
when required
- Re-iterates parameter preconditions and special cases within the
parameter documentation itself (might also help towards #9805?)
- Fixes contradictions within return value documentation
- Adds missing parameter documentation on `init()`.
aba75be827