Pull request:* all: fix all staticcheck SA warnings

Merge in DNS/adguard-home from 2238-fix-static-analisys-warnings to master

Squashed commit of the following:

commit 721ca6fa1cbfdfe9d414e6ed52fec4a64653fb52
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Oct 30 15:48:10 2020 +0300

    * all: fix all staticcheck SA warnings

    Closes #2238.

internal/dhcpd/dhcp_http.go

@@ -175,7 +175,7 @@ func (s *Server) handleDHCPSetConfig(w http.ResponseWriter, r *http.Request) {
 		v6conf.InterfaceName = newconfig.InterfaceName
 		v6conf.notify = s.onNotify
 		s6, err = v6Create(v6conf)
-		if s6 == nil {
+		if err != nil {
 			httpError(r, w, http.StatusBadRequest, "Invalid DHCPv6 configuration: %s", err)
 			return
 		}

internal/dhcpd/dhcpd_test.go

@@ -83,7 +83,6 @@ func TestIsValidSubnetMask(t *testing.T) {
 func TestNormalizeLeases(t *testing.T) {
 	dynLeases := []*Lease{}
 	staticLeases := []*Lease{}
-	leases := []*Lease{}
 
 	lease := &Lease{}
 	lease.HWAddr = []byte{1, 2, 3, 4}
@@ -100,7 +99,7 @@ func TestNormalizeLeases(t *testing.T) {
 	lease.HWAddr = []byte{2, 2, 3, 4}
 	staticLeases = append(staticLeases, lease)
 
-	leases = normalizeLeases(staticLeases, dynLeases)
+	leases := normalizeLeases(staticLeases, dynLeases)
 
 	assert.True(t, len(leases) == 3)
 	assert.True(t, bytes.Equal(leases[0].HWAddr, []byte{1, 2, 3, 4}))

internal/dhcpd/v6.go

@@ -45,6 +45,7 @@ func ip6InRange(start net.IP, ip net.IP) bool {
 	if len(start) != 16 {
 		return false
 	}
+	//lint:ignore SA1021 TODO(e.burkov): Ignore this for now, think about using masks.
 	if !bytes.Equal(start[:15], ip[:15]) {
 		return false
 	}