[9.20] fix: usr: Use IPv6 queries in delv +ns

[9.20] fix: usr: Use IPv6 queries in delv +ns

`delv +ns` invokes the same code to perform name resolution as `named`,
but it neglected to set up an IPv6 dispatch object first. Consequently,
it was behaving more like `named -4`. It now sets up dispatch objects
for both address families, and performs resolver queries to both v4 and v6
addresses, except when one of the address families has been suppressed
by using `delv -4` or `delv -6`.

Closes #5352

Backport of MR !10563

Merge branch 'backport-5352-delv-ipv6-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!10573