ipn/ipnlocal: add localNodeContext with netmap-related fields and methods

Updates #12614

Signed-off-by: Nick Khyl <nickk@tailscale.com>

ipn/ipnlocal/web_client.go

@@ -116,11 +116,12 @@ func (b *LocalBackend) handleWebClientConn(c net.Conn) error {
 // for each of the local device's Tailscale IP addresses. This is needed to properly
 // route local traffic when using kernel networking mode.
 func (b *LocalBackend) updateWebClientListenersLocked() {
-	if b.netMap == nil {
+	nm := b.currentNode().NetMap()
+	if nm == nil {
 		return
 	}
 
-	addrs := b.netMap.GetAddresses()
+	addrs := nm.GetAddresses()
 	for _, pfx := range addrs.All() {
 		addrPort := netip.AddrPortFrom(pfx.Addr(), webClientPort)
 		if _, ok := b.webClientListeners[addrPort]; ok {