Pull request: dhcpd: add ips and text option types

Updates #2385.

Squashed commit of the following:

commit ce8467f1c013c6b3fef59667084e2c6569a7213c
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Mar 15 19:02:17 2021 +0300

    dhcpd: add ips and text option types

internal/dhcpd/dhcpd.go

@@ -2,18 +2,14 @@
 package dhcpd
 
 import (
-	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"net"
 	"net/http"
 	"path/filepath"
 	"runtime"
-	"strconv"
-	"strings"
 	"time"
 
-	"github.com/AdguardTeam/AdGuardHome/internal/util"
 	"github.com/AdguardTeam/golibs/log"
 )
 
@@ -283,48 +279,3 @@ func (s *Server) FindMACbyIP(ip net.IP) net.HardwareAddr {
 func (s *Server) AddStaticLease(lease Lease) error {
 	return s.srv4.AddStaticLease(lease)
 }
-
-// Parse option string
-// Format:
-// CODE TYPE VALUE
-func parseOptionString(s string) (uint8, []byte) {
-	s = strings.TrimSpace(s)
-	scode := util.SplitNext(&s, ' ')
-	t := util.SplitNext(&s, ' ')
-	sval := util.SplitNext(&s, ' ')
-
-	code, err := strconv.Atoi(scode)
-	if err != nil || code <= 0 || code > 255 {
-		return 0, nil
-	}
-
-	var val []byte
-
-	switch t {
-	case "hex":
-		val, err = hex.DecodeString(sval)
-		if err != nil {
-			return 0, nil
-		}
-	case "ip":
-		ip := net.ParseIP(sval)
-		if ip == nil {
-			return 0, nil
-		}
-
-		// Most DHCP options require IPv4, so do not put the 16-byte
-		// version if we can.  Otherwise, the clients will receive weird
-		// data that looks like four IPv4 addresses.
-		//
-		// See https://github.com/AdguardTeam/AdGuardHome/issues/2688.
-		if ip4 := ip.To4(); ip4 != nil {
-			val = ip4
-		} else {
-			val = ip
-		}
-	default:
-		return 0, nil
-	}
-
-	return uint8(code), val
-}