Snapserver expects the arguments `--tcp.bind_to_address` and
`--http.bind_to_address` instead of the `--tcp.address` (and http
equivalent) versions.
This caused the process to listen on `0.0.0.0` (for TCP and HTTP
sockets) regardless of the configuration value. It also never listend on
the IPv6 address `::` as our module system made the user believe.
This commit fixes the above issue and ensures that (at least for the TCP
socket) that our default `::` does indeed allow connections via IPv6
(to localhost aka ::1).
c9c93b0add