Fix golint warnings (#4241)

Include:
1. plugin/forward/type.go:8:2: const typeUdp should be typeUDP
2. plugin/forward/type.go:9:2: const typeTcp should be typeTCP
3. plugin/forward/type.go:10:2: const typeTls should be typeTLS
4. plugin/kubernetes/metrics.go:24:2: var DnsProgrammingLatency should be DNSProgrammingLatency
5. plugin/kubernetes/metrics_test.go:124:102: func parameter clusterIp should be clusterIP

Signed-off-by: zouyu <zouy.fnst@cn.fujitsu.com>

plugin/forward/persistent_test.go

@@ -96,14 +96,14 @@ func TestCleanupAll(t *testing.T) {
 	c2, _ := dns.DialTimeout("udp", tr.addr, maxDialTimeout)
 	c3, _ := dns.DialTimeout("udp", tr.addr, maxDialTimeout)
 
-	tr.conns[typeUdp] = []*persistConn{{c1, time.Now()}, {c2, time.Now()}, {c3, time.Now()}}
+	tr.conns[typeUDP] = []*persistConn{{c1, time.Now()}, {c2, time.Now()}, {c3, time.Now()}}
 
-	if len(tr.conns[typeUdp]) != 3 {
+	if len(tr.conns[typeUDP]) != 3 {
 		t.Error("Expected 3 connections")
 	}
 	tr.cleanup(true)
 
-	if len(tr.conns[typeUdp]) > 0 {
+	if len(tr.conns[typeUDP]) > 0 {
 		t.Error("Expected no cached connections")
 	}
 }

plugin/forward/type.go

@@ -5,33 +5,33 @@ import "net"
 type transportType int
 
 const (
-	typeUdp transportType = iota
-	typeTcp
-	typeTls
+	typeUDP transportType = iota
+	typeTCP
+	typeTLS
 	typeTotalCount // keep this last
 )
 
 func stringToTransportType(s string) transportType {
 	switch s {
 	case "udp":
-		return typeUdp
+		return typeUDP
 	case "tcp":
-		return typeTcp
+		return typeTCP
 	case "tcp-tls":
-		return typeTls
+		return typeTLS
 	}
 
-	return typeUdp
+	return typeUDP
 }
 
 func (t *Transport) transportTypeFromConn(pc *persistConn) transportType {
 	if _, ok := pc.c.Conn.(*net.UDPConn); ok {
-		return typeUdp
+		return typeUDP
 	}
 
 	if t.tlsConfig == nil {
-		return typeTcp
+		return typeTCP
 	}
 
-	return typeTls
+	return typeTLS
 }