Pull request: 3225 bsd dhcp

Merge in DNS/adguard-home from 3225-bsd-dhcp to master

Closes #3225.
Closes #3417.

Squashed commit of the following:

commit e7ea691824c7ebc8cafd8c9e206679346cbc8592
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 17:02:02 2021 +0300

    all: imp code, docs

commit 5b598fc18a9b69a0256569f4c691bb6a2193dfbd
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 16:28:12 2021 +0300

    all: mv logic, imp code, docs, log changes

commit e3e1577a668fe3e5c61d075c390e4bd7268181ba
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 14:15:10 2021 +0300

    dhcpd: imp checkother

commit 3cc8b058195c30a7ef0b7741ee8463270d9e47ff
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Aug 11 13:20:18 2021 +0300

    all: imp bsd support

internal/dhcpd/v6.go

@@ -10,6 +10,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/log"
 	"github.com/AdguardTeam/golibs/netutil"
@@ -607,7 +608,12 @@ func (s *v6Server) Start() (err error) {
 
 	log.Debug("dhcpv6: starting...")
 
-	dnsIPAddrs, err := ifaceDNSIPAddrs(iface, ipVersion6, defaultMaxAttempts, defaultBackoff)
+	dnsIPAddrs, err := aghnet.IfaceDNSIPAddrs(
+		iface,
+		aghnet.IPVersion6,
+		defaultMaxAttempts,
+		defaultBackoff,
+	)
 	if err != nil {
 		return fmt.Errorf("interface %s: %w", ifaceName, err)
 	}