net: add examples for IPv4, ParseCIDR & IPv4Mask

Further examples to support the net package.

See issue #5757

Change-Id: I839fd97a468c8d9195e8f4a0ee886ba50ca3f382
Reviewed-on: https://go-review.googlesource.com/42912Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/example_test.go

@@ -36,6 +36,35 @@ func ExampleListener() {
 	}
 }
 
+func ExampleIPv4() {
+	fmt.Println(net.IPv4(8, 8, 8, 8))
+
+	// Output:
+	// 8.8.8.8
+}
+
+func ExampleParseCIDR() {
+	ipv4Addr, ipv4Net, err := net.ParseCIDR("192.0.2.1/16")
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(ipv4Addr)
+	fmt.Println(ipv4Net)
+
+	ipv6Addr, ipv6Net, err := net.ParseCIDR("2001:db8:a0b:12f0::1/32")
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(ipv6Addr)
+	fmt.Println(ipv6Net)
+
+	// Output:
+	// 192.0.2.1
+	// 192.0.0.0/16
+	// 2001:db8:a0b:12f0::1
+	// 2001:db8::/32
+}
+
 func ExampleCIDRMask() {
 	// This mask corresponds to a /31 subnet for IPv4.
 	fmt.Println(net.CIDRMask(31, 32))
@@ -47,3 +76,10 @@ func ExampleCIDRMask() {
 	// fffffffe
 	// ffffffffffffffff0000000000000000
 }
+
+func ExampleIPv4Mask() {
+	fmt.Println(net.IPv4Mask(255, 255, 255, 0))
+
+	// Output:
+	// ffffff00
+}