ipv4: don't refer internal packages in examples

Updates golang/go#12163.

Change-Id: I1cd3b6324eb37d7a2285683590acd188758e7d90
Reviewed-on: https://go-review.googlesource.com/13654
Reviewed-by: Ian Lance Taylor <iant@golang.org>

ipv4/example_test.go

@@ -13,7 +13,6 @@ import (
 	"time"
 
 	"golang.org/x/net/icmp"
-	"golang.org/x/net/internal/iana"
 	"golang.org/x/net/ipv4"
 )
 
@@ -32,7 +31,7 @@ func ExampleConn_markingTCP() {
 		go func(c net.Conn) {
 			defer c.Close()
 			p := ipv4.NewConn(c)
-			if err := p.SetTOS(iana.DiffServAF11); err != nil {
+			if err := p.SetTOS(0x28); err != nil { // DSCP AF11
 				log.Fatal(err)
 			}
 			if err := p.SetTTL(128); err != nil {
@@ -102,7 +101,7 @@ func ExamplePacketConn_tracingIPPacketRoute() {
 		log.Fatal("no A record found")
 	}
 
-	c, err := net.ListenPacket(fmt.Sprintf("ip4:%d", iana.ProtocolICMP), "0.0.0.0") // ICMP for IPv4
+	c, err := net.ListenPacket("ip4:1", "0.0.0.0") // ICMP for IPv4
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -149,7 +148,7 @@ func ExamplePacketConn_tracingIPPacketRoute() {
 			}
 			log.Fatal(err)
 		}
-		rm, err := icmp.ParseMessage(iana.ProtocolICMP, rb[:n])
+		rm, err := icmp.ParseMessage(1, rb[:n])
 		if err != nil {
 			log.Fatal(err)
 		}
@@ -173,7 +172,7 @@ func ExamplePacketConn_tracingIPPacketRoute() {
 }
 
 func ExampleRawConn_advertisingOSPFHello() {
-	c, err := net.ListenPacket(fmt.Sprintf("ip4:%d", iana.ProtocolOSPFIGP), "0.0.0.0") // OSPF for IPv4
+	c, err := net.ListenPacket("ip4:89", "0.0.0.0") // OSPF for IPv4
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -201,10 +200,10 @@ func ExampleRawConn_advertisingOSPFHello() {
 	iph := &ipv4.Header{
 		Version:  ipv4.Version,
 		Len:      ipv4.HeaderLen,
-		TOS:      iana.DiffServCS6,
+		TOS:      0xc0, // DSCP CS6
 		TotalLen: ipv4.HeaderLen + len(ospf),
 		TTL:      1,
-		Protocol: iana.ProtocolOSPFIGP,
+		Protocol: 89,
 		Dst:      allSPFRouters.IP.To4(),
 	}