Add a wrapper that uses anet on Android, but net on other platforms.
### Purpose
Fixes
https://forum.syncthing.net/t/workaround-for-android-local-discovery/20403/12
### Testing
Run two Syncthing instances with Global Discovery disabled. Pair them
with each other, don't hardcode their addresses, and verify they
connect.
Fixes#7403.
Tested by enabling UPnP on the router, and checking on the router page
that the external ports of the UDP mappings match what is shown in the
logs and the internal ports matching the QUIC listening port.
### Testing
Change the `auditEnabled` option and you should get a prompt in the Web
GUI.
Restart and change the `auditFile` option, and you should get that same
prompt.
The prompt you should get is shown in the screenshots below.
### Screenshots

Co-authored-by: Jakob Borg <jakob@kastelo.net>