install/57244: sysinst ignores manually-supplied DNS server address

[tgl%sss.pgh.pa.us@localhost]

>Number:         57244
>Category:       install
>Synopsis:       sysinst ignores manually-supplied DNS server address
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 25 20:45:00 +0000 2023
>Originator:     Tom Lane
>Release:        10.0_BETA 202302240730Z snapshot
>Organization:
>Environment:
NetBSD sss2.sss.pgh.pa.us 10.0_BETA NetBSD 10.0_BETA (SD0) #0: Fri Feb 24 15:31:21 EST 2023  tgl%nuc1.sss.pgh.pa.us@localhost:/home/tgl/netbsd-10-202302240730Z/obj.hppa/sys/arch/hppa/compile/SD0 hppa
>Description:
If I allow sysinst's "Configure network" dialog to do autoconfiguration, and then manually override its choice of DNS server address, it ignores the manual entry when setting up its own /etc/resolv.conf, so that later sysinst operations such as fetching distribution files from an NFS server may be unable to resolve DNS names as expected.

I've only encountered this in the context of doing the "b) Upgrade NetBSD" option, which won't attempt to modify the target installation's /etc/resolv.conf.  So I'm not sure whether the wrong server address would also get written into that during a normal install.  If it does write the correct address there then many people wouldn't notice the issue.

This is a fairly new bug --- I last did this type of thing with the 10.0 202212262100Z snapshot, and it behaved correctly then.

Also, there may be an IPv4 vs IPv6 issue here: autoconfiguration is seizing on an IPv6 DNS server address, which I think is being offered (against my wishes) by my Verizon router, and ignoring the IPv4 DNS server addresses offered by my DHCP server.  Then when I manually put in the IPv4 address I want it to use, it's ignoring that in favor of the IPv6 address.  This results in a failure since the Verizon router knows nothing of the local machine I want to do an NFS installation from.
>How-To-Repeat:
See above.  You may need a mixed IPv4/v6 environment.  I got to the "Configure network" dialog from the fetch-distribution-files-from-NFS dialog, but I doubt that the exact path matters too much.  After mount complained that it can't get an IP address for the given NFS host name, I control-Z'd sysinst and looked at /etc/resolv.conf to see that it contained the unwanted IPv6 address and not the wanted IPv4 one.  (Thanks to Martin Husemann for that debugging suggestion.)
>Fix: