Pull request 1798: 4262-ipv6-pref

Updates #4262.

Squashed commit of the following:

commit de64f9c40c00317dbb5dbdda900d9b4c574a0a32
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Apr 3 19:23:15 2023 +0300

    all: add ipv6 boostrap pref

internal/dnsforward/dnsforward.go

@@ -447,6 +447,8 @@ func (s *Server) setupResolvers(localAddrs []string) (err error) {
 			Bootstrap: bootstraps,
 			Timeout:   defaultLocalTimeout,
 			// TODO(e.burkov): Should we verify server's certificates?
+
+			PreferIPv6: s.conf.BootstrapPreferIPv6,
 		},
 	)
 	if err != nil {