Kernel: Add support for route flags

Previously the routing table did not store the route flags. This
adds basic support and exposes them in the /proc directory so that a
userspace caller can query the route and identify the type of each
route.

Kernel/GlobalProcessExposed.cpp

@@ -114,6 +114,7 @@ private:
                 TRY(obj.add("gateway", gateway->view()));
                 auto netmask = TRY(it.netmask.to_string());
                 TRY(obj.add("genmask", netmask->view()));
+                TRY(obj.add("flags", it.flags));
                 TRY(obj.add("interface", it.adapter->name()));
                 TRY(obj.finish());
             }