net: don't return nil interface address on netbsd

On NetBSD routing sockaddrs for interface address contain sockaddr_dl.

R=dave, rsc
CC=golang-dev
https://golang.org/cl/7085064

src/pkg/net/interface_bsd.go

@@ -118,10 +118,12 @@ func interfaceAddrTable(ifindex int) ([]Addr, error) {
 				if err != nil {
 					return nil, err
 				}
+				if ifa != nil {
 					ifat = append(ifat, ifa)
 				}
 			}
 		}
+	}
 	return ifat, nil
 }
 
@@ -157,6 +159,8 @@ func newAddr(m *syscall.InterfaceAddrMessage) (Addr, error) {
 					ifa.IP[2], ifa.IP[3] = 0, 0
 				}
 			}
+		default: // Sockaddrs contain syscall.SockaddrDatalink on NetBSD
+			return nil, nil
 		}
 	}
 	return ifa, nil

src/pkg/net/interface_test.go

@@ -75,9 +75,13 @@ func testInterfaceMulticastAddrs(t *testing.T, ifi *Interface) {
 
 func testAddrs(t *testing.T, ifat []Addr) {
 	for _, ifa := range ifat {
-		switch ifa.(type) {
+		switch v := ifa.(type) {
 		case *IPAddr, *IPNet:
+			if v == nil {
+				t.Errorf("\tunexpected value: %v", ifa)
+			} else {
 				t.Logf("\tinterface address %q", ifa.String())
+			}
 		default:
 			t.Errorf("\tunexpected type: %T", ifa)
 		}
@@ -86,9 +90,13 @@ func testAddrs(t *testing.T, ifat []Addr) {
 
 func testMulticastAddrs(t *testing.T, ifmat []Addr) {
 	for _, ifma := range ifmat {
-		switch ifma.(type) {
+		switch v := ifma.(type) {
 		case *IPAddr:
+			if v == nil {
+				t.Errorf("\tunexpected value: %v", ifma)
+			} else {
 				t.Logf("\tjoined group address %q", ifma.String())
+			}
 		default:
 			t.Errorf("\tunexpected type: %T", ifma)
 		}