Nanostack changes for PPP service

Created PPP interface for PPP service. Re-used the ethernet tasklet
and PHY driver structure for PPP.

Author: Mika Leppänen

features/nanostack/mbed-mesh-api/mbed-mesh-api/MeshInterfaceNanostack.h

@@ -34,7 +34,10 @@ class Nanostack::Interface : public OnboardNetworkStack::Interface, private mbed
 
     void get_mac_address(uint8_t *buf) const
     {
-        interface_phy.get_mac_address(buf);
+        NanostackMACPhy *phy = interface_phy.nanostack_mac_phy();
+        if (phy) {
+            phy->get_mac_address(buf);
+        }
     }
 
     /**

features/nanostack/mbed-mesh-api/mbed-mesh-api/NanostackPPPInterface.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2019 ARM Limited. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ * Licensed under the Apache License, Version 2.0 (the License); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef NANOSTACKPPPINTERFACE_H
+#define NANOSTACKPPPINTERFACE_H
+
+#include "MeshInterfaceNanostack.h"
+#include "PPPInterface.h"
+#include "NanostackPPPPhy.h"
+
+class Nanostack::PPPInterface : public Nanostack::Interface {
+public:
+    virtual nsapi_error_t bringup(bool dhcp, const char *ip,
+                                  const char *netmask, const char *gw,
+                                  nsapi_ip_stack_t stack = DEFAULT_STACK,
+                                  bool blocking = true);
+    virtual nsapi_error_t bringdown();
+
+    typedef mbed::Callback<void (uint8_t up, int8_t device_id)> link_state_cb_t;
+    virtual void set_link_state_changed_callback(link_state_cb_t link_state_cb);
+
+private:
+    friend class Nanostack;
+    PPPInterface(NanostackPhy &phy) : Interface(phy), link_state_up(false), enet_tasklet_connected(false) {}
+    nsapi_error_t initialize();
+    void link_state_changed(bool up);
+    nsapi_error_t connect_enet_tasklet();
+    link_state_cb_t link_state_cb;
+    bool link_state_up;
+    bool enet_tasklet_connected;
+};
+
+#endif