vlan: parent device integration + networking plan doc update

VlanDevice gains devices: Rc<RefCell<DeviceList>> field. send()
now forwards tagged frames to parent device via the shared list,
instead of dropping them (R43 drop fix) or self-looping (original).

Constructor changed: VlanDevice::new(name, parent, vlan_id, devices).

netfilter/netcfg/route: direct routes + flush + version + help
docs: NETWORKING-IMPROVEMENT-PLAN.md updated with Phase 4
completion status (firewall/conntrack/NAT) and Phase 6 VLAN status.

All 31 tests pass.

netstack/src/link/vlan.rs

@@ -9,6 +9,7 @@
 //! the 4-byte 802.1Q tag (TPID 0x8100 + TCI) before/after the Ethernet
 //! header on each frame.
 
+use std::cell::RefCell;
 use std::collections::VecDeque;
 use std::rc::Rc;
 
@@ -17,13 +18,14 @@ use smoltcp::wire::{
     EthernetAddress, EthernetFrame, EthernetProtocol, IpAddress, IpCidr,
 };
 
-use super::LinkDevice;
+use super::{DeviceList, LinkDevice};
 
 const TPID_8021Q: u16 = 0x8100;
 
 pub struct VlanDevice {
     name: Rc<str>,
     parent_name: Rc<str>,
+    devices: Rc<RefCell<DeviceList>>,
     vlan_id: u16,
     priority: u8,
     tag: [u8; 4],
@@ -35,7 +37,7 @@ pub struct VlanDevice {
 }
 
 impl VlanDevice {
-    pub fn new(name: &str, parent_name: &str, vlan_id: u16) -> Self {
+    pub fn new(name: &str, parent_name: &str, vlan_id: u16, devices: Rc<RefCell<DeviceList>>) -> Self {
         let tci: u16 = vlan_id & 0x0fff;
         let tag: [u8; 4] = [
             (TPID_8021Q >> 8) as u8,
@@ -46,6 +48,7 @@ impl VlanDevice {
         Self {
             name: name.into(),
             parent_name: parent_name.into(),
+            devices,
             vlan_id,
             priority: 0,
             tag,
@@ -117,13 +120,17 @@ impl VlanDevice {
 }
 
 impl LinkDevice for VlanDevice {
-    fn send(&mut self, next_hop: IpAddress, packet: &[u8], _now: Instant) {
-        // The VLAN device has no parent device reference, so we cannot
-        // send the tagged frame out. Log and drop the packet rather than
-        // creating a self-loop (which would re-deliver the packet to
-        // recv() and never reach a real interface).
-        log::debug!("vlan: dropping {} byte frame (no parent device)", packet.len());
-        let _ = next_hop;
+    fn send(&mut self, next_hop: IpAddress, packet: &[u8], now: Instant) {
+        let tagged = self.insert_tag(packet).to_vec();
+        // Forward the tagged frame to the parent device by looking it
+        // up in the shared device list. If the parent doesn't exist or
+        // isn't ready, drop the packet with a debug log.
+        if let Some(parent) = self.devices.borrow_mut().get_mut(&self.parent_name) {
+            parent.send(next_hop, &tagged, now);
+        } else {
+            log::debug!("vlan: parent {} not found, dropping {} byte frame",
+                self.parent_name, packet.len());
+        }
     }
 
     fn recv(&mut self, _now: Instant) -> Option<&[u8]> {