Allow ThreadInterface::device_eui64_get() before connect()

Perform necessary driver initialisation so that we can read
the EUI-64 before connecting.

Fixes #7391.

features/nanostack/mbed-mesh-api/source/MeshInterfaceNanostack.cpp

@@ -102,15 +102,20 @@ int InterfaceNanostack::disconnect()
 
 nsapi_error_t MeshInterfaceNanostack::initialize(NanostackRfPhy *phy)
 {
-    if (_phy) {
+    if (_phy && phy && _phy != phy) {
         error("Phy already set");
         return NSAPI_ERROR_IS_CONNECTED;
     }
-    _phy = phy;
+    if (phy) {
-    return NSAPI_ERROR_OK;
+        _phy = phy;
+    }
+    if (_phy) {
+        return do_initialize();
+    } else {
+        return NSAPI_ERROR_PARAMETER;
+    }
 }
 
-
 void Nanostack::Interface::network_handler(mesh_connection_status_t status)
 {
     if ((status == MESH_CONNECTED || status == MESH_CONNECTED_LOCAL ||
@@ -148,7 +153,9 @@ nsapi_error_t Nanostack::Interface::register_phy()
 {
     NanostackLockGuard lock;
 
-    _device_id = interface_phy.phy_register();
+    if (_device_id < 0) {
+        _device_id = interface_phy.phy_register();
+    }
     if (_device_id < 0) {
         return NSAPI_ERROR_DEVICE_ERROR;
     }

features/nanostack/mbed-mesh-api/source/ThreadInterface.cpp

@@ -213,6 +213,10 @@ void ThreadInterface::device_eui64_set(const uint8_t *eui64)
 
 void ThreadInterface::device_eui64_get(uint8_t *eui64)
 {
+    memset(eui64, 0, 8);
+    if (!get_interface()) {
+        return;
+    }
     get_interface()->device_eui64_get(eui64);
 }
 
@@ -226,6 +230,9 @@ void Nanostack::ThreadInterface::device_eui64_get(uint8_t *eui64)
 {
     if (!eui64_set) {
         uint8_t eui64_buf[8];
+        if (register_phy() < 0) {
+            return;
+        }
         get_phy().get_mac_address(eui64_buf);
         device_eui64_set(eui64_buf);
     }