Enable C++20 for netd

This is mainly so we can use safer buffer management constructs built
around std::span and std::ranges, along with other goodies such as
std::expected. C++20 is not yet finalized, but we're not planning to use
any advanced features at this stage.

Change-Id: I8e880a010422ac705824fb8b7e519b8a76802a5d
1 file changed