This fixes the deadlock by reducing where we hold the various locks. To
start with it splits up the existing "mut" into a "listenersMut" and a
"curConMut" as these are the two things being protected and I can see no
relation between them that requires a shared lock. It also moves all
model calls outside of the lock, as I see no reason to hold the lock
while calling the model (and it's risky, as proven).
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3069
1. Removes separate relay lists and relay clients/services, just makes it a listen address
2. Easier plugging-in of other transports
3. Allows "hot" disabling and enabling NAT services
4. Allows "hot" listen address changes
5. Changes listen address list with a preferable "default" value just like for discovery
6. Debounces global discovery announcements as external addresses change (which it might alot upon starting)
7. Stops this whole "pick other peers relay by latency". This information is no longer available,
but I don't think it matters as most of the time other peer only has one relay.
8. Rename ListenAddress to ListenAddresses, as well as in javascript land.
9. Stop serializing deprecated values to JSON
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/2982
