bind: don't break IPv6 support

bind: don't break IPv6 support

What started in #20183 as a attempt to clean up noise in the logfiles,
turned out to be causing denial-of-service for dual-stack and especially
IPv6-only environments.

Breaking core network functionality cannot possibly be less important
than cosmetic issues, and those affected by log spam can avoid it via
other means (e.g. "query-source-v6 none;" in named.conf).

There's no reliable heuristic for determining whether there's IPv6
connectivity at the time bind is started which will catch any and all
corner cases, as discussed in #26327.

So, remove this logic for now. If a suitable heuristic can be devised,
it can always be added in a subsequent patch, but I have my doubts.

(Also, quote one variable to make shellcheck happy)

Closes: #26327
Closes: #20468
Signed-off-by: David Härdeman <[email protected]>