TBR third_party mdns: stop relying on struct exported by net.

Actually labeling the fields in the initializer works but I decided
to remove the reliance altogether on my github project so we should
copy that here.

Change-Id: If27d75a327d6a71458d76d54f55e455bd5a530ac
diff --git a/go/src/github.com/presotto/go-mdns-sd/go_dns/dial.go b/go/src/github.com/presotto/go-mdns-sd/go_dns/dial.go
index 5e7fae3..6f5ba80 100644
--- a/go/src/github.com/presotto/go-mdns-sd/go_dns/dial.go
+++ b/go/src/github.com/presotto/go-mdns-sd/go_dns/dial.go
@@ -6,6 +6,7 @@
 package dns
 
 import (
+	"errors"
 	netpkg "net"
 	"strings"
 )
@@ -78,7 +79,7 @@
 	case *netpkg.IPAddr:
 		c, err = netpkg.DialIP(net, nil, ra)
 	default:
-		err = &netpkg.OpError{"dial", net + " " + addr, nil, netpkg.UnknownNetworkError(net)}
+		err = errors.New("Unknown network address type")
 	}
 	if err != nil {
 		return nil, err