netcfg: UDP socket listing + routes/count node

- UDP sockets now enumerated in /scheme/netcfg/sockets/list:
    udp: local=0.0.0.0:53
    udp: local=127.0.0.1:8080
- New RouteTable::len() method + /scheme/netcfg/route/count:
    cat /scheme/netcfg/route/count  →  'routes: 4'

Complete connections view now covers TCP + UDP listening sockets,
plus route count summary for at-a-glance monitoring.

netstack/src/router/route_table.rs

@@ -130,6 +130,10 @@ impl RouteTable {
             rule.src = new_src;
         }
     }
+
+    pub fn len(&self) -> usize {
+        self.rules.len()
+    }
 }
 
 impl Display for RouteTable {

netstack/src/scheme/netcfg/mod.rs

@@ -183,6 +183,15 @@ fn mk_root_node(
                                 local.map(|e| format!("{}", e)).unwrap_or_else(|| "-".to_string()),
                                 remote.map(|e| format!("{}", e)).unwrap_or_else(|| "-".to_string())));
                         }
+                        if let smoltcp::socket::Socket::Udp(udp_sock) = socket {
+                            let endpoint = udp_sock.endpoint();
+                            out.push_str(&format!("udp: local={}\n",
+                                if endpoint.port != 0 {
+                                    format!("{}", endpoint)
+                                } else {
+                                    "-".to_string()
+                                }));
+                        }
                     }
                     out
                 }
@@ -251,6 +260,12 @@ fn mk_root_node(
                     format!("{}", route_table.borrow())
                 }
             },
+            "count" => {
+                ro [route_table] || {
+                    let count = route_table.borrow().len();
+                    format!("routes: {}\n", count)
+                }
+            },
             "add" => {
                 wo [iface, notifier, route_table] (Option<Rule>, None)
                 |cur_value, line| {