local-unbound-setup: Set so-sndbuf to 0

[des]

Summary

Without this setting, Unbound 1.24.0 and newer will attempt to set the
socket buffer size to 4 MB to mitigate issues that mostly affect servers
with large numbers of clients on local networks, which is not a scenario
local-unbound is intended for. This is not only a waste of resources,
it can also fail, resulting in a warning message on daemon startup.

[jlduran]

Thank you!

[cy]

Less intrusive.