Currently, only configuration sources and providers of addresses and
routes are serialized/deserialized.
This should mostly not change behavior, as dynamic (except for DHCPv4)
configurations will be dropped before stopping networkd, and for DHCPv4
protocol, we have already had another logic to handle DHCPv4
configurations.
Preparation for later commits.
This is preparation for making our Varlink API a public API. Since our
Varlink API is built on top of our JSON API we need to make that public
first (it's a nice API, but JSON APIs there are already enough, this is
purely about the Varlink angle).
I made most of the json.h APIs public, and just placed them in
sd-json.h. Sometimes I wasn't so sure however, since the underlying data
structures would have to be made public too. If in doubt I didn#t risk
it, and moved the relevant API to src/libsystemd/sd-json/json-util.h
instead (without any sd_* symbol prefixes).
This is mostly a giant search/replace patch.