PPP, SERVER: added PPPoS server support

New function: ppp_listen(), listen for an incoming PPP connection.

src/include/netif/ppp/ppp.h

@@ -463,6 +463,21 @@ void ppp_set_notify_phase_callback(ppp_pcb *pcb, ppp_notify_phase_cb_fn notify_p
  */
 err_t ppp_open(ppp_pcb *pcb, u16_t holdoff);
 
+#if PPP_SERVER
+/*
+ * Listen for an incoming PPP connection.
+ *
+ * This can only be called if PPP is in the dead phase.
+ *
+ * Local and remote interface IP addresses, as well as DNS are
+ * provided through a previously filled struct ppp_addrs.
+ *
+ * If this port connects to a modem, the modem connection must be
+ * established before calling this.
+ */
+err_t ppp_listen(ppp_pcb *pcb, struct ppp_addrs *addrs);
+#endif /* PPP_SERVER */
+
 /*
  * Initiate the end of a PPP connection.
  * Any outstanding packets in the queues are dropped.

src/include/netif/ppp/ppp_impl.h

@@ -143,6 +143,10 @@
 struct link_callbacks {
   /* Start a connection (e.g. Initiate discovery phase) */
   err_t (*connect) (ppp_pcb *pcb, void *ctx);
+#if PPP_SERVER
+  /* Listen for an incoming connection (Passive mode) */
+  err_t (*listen) (ppp_pcb *pcb, void *ctx, struct ppp_addrs *addrs);
+#endif /* PPP_SERVER */
   /* End a connection (i.e. initiate disconnect phase) */
   void (*disconnect) (ppp_pcb *pcb, void *ctx);
   /* Free lower protocol control block */