network/route: accept an empty network address as the destination.

* linux + BSD accept 0.0.0.0 or :: as the default route identifier
* openvpn passes 0.0.0.0 as the default route
* our own route command shows "0.0.0.0" for the default route

Lets not be special here, and do what everyone else does. default
still works for backwards compat.

This uncovered a potental bug in BNetworkAddress. See #19296

Change-Id: I3aea99cae4cf9c52142cb97e2a06b8432de294b9
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8592
Reviewed-by: Adrien Destugues <[email protected]>
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: Fredrik Holmqvist <[email protected]>
Reviewed-by: Alexander von Gluck <[email protected]>
Haiku-Format: Haiku-format Bot <[email protected]>

src/bin/network/route/route.cpp

@@ -431,6 +431,10 @@ main(int argc, char** argv)
 			i++;
 			break;
 		} else if (parse_address(familyIndex, argv[i], destination)) {
+			if (destination.IsEmpty()) {
+				defaultRoute = true;
+				route.flags = RTF_DEFAULT;
+			}
 			i++;
 			break;
 		}