Pull request: 2582 invalid hostname vol.3

Merge in DNS/adguard-home from 2582-zero-byte to master

Updates #2582.

Squashed commit of the following:

commit 88db23f26cd6ee9978310c7030f6866b9ef58785
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Mar 11 13:01:02 2021 +0300

    dhcpd: rm temporary workaround

internal/dhcpd/v6.go

@@ -46,7 +46,8 @@ func ip6InRange(start, ip net.IP) bool {
 	if len(start) != 16 {
 		return false
 	}
-	//lint:ignore SA1021 TODO(e.burkov): Ignore this for now, think about using masks.
+	//lint:ignore SA1021 TODO(e.burkov): Ignore this for now, think about
+	// using masks.
 	if !bytes.Equal(start[:15], ip[:15]) {
 		return false
 	}