Ensure to set Extended Address's local bit (#1711)

* Create a new `GenerateExtAddress()` method;

* Fix the issue that the extended address U/L bit may not be set, which is generated after join success.

src/core/mac/mac.cpp

@@ -154,13 +154,7 @@ Mac::Mac(ThreadNetif &aThreadNetif):
     mTxFrame(static_cast<Frame *>(otPlatRadioGetTransmitBuffer(aThreadNetif.GetInstance()))),
     mKeyIdMode2FrameCounter(0)
 {
-    for (size_t i = 0; i < sizeof(mExtAddress); i++)
-    {
-        mExtAddress.m8[i] = static_cast<uint8_t>(otPlatRandomGet());
-    }
-
-    mExtAddress.SetGroup(false);
-    mExtAddress.SetLocal(true);
+    GenerateExtAddress(&mExtAddress);
 
     ClearNoiseFloorAverage(mNoiseFloor);
 
@@ -434,6 +428,17 @@ void Mac::SetRxOnWhenIdle(bool aRxOnWhenIdle)
     }
 }
 
+void Mac::GenerateExtAddress(ExtAddress *aExtAddress)
+{
+    for (size_t i = 0; i < sizeof(ExtAddress); i++)
+    {
+        aExtAddress->m8[i] = static_cast<uint8_t>(otPlatRandomGet());
+    }
+
+    aExtAddress->SetGroup(false);
+    aExtAddress->SetLocal(true);
+}
+
 void Mac::SetExtAddress(const ExtAddress &aExtAddress)
 {
     uint8_t buf[sizeof(aExtAddress)];

src/core/mac/mac.hpp

@@ -348,6 +348,14 @@ public:
      */
     ThreadError SendFrameRequest(Sender &aSender);
 
+    /**
+     * This method generates a random IEEE 802.15.4 Extended Address.
+     *
+     * @param[out]  aExtAddress  A pointer to where the generated Extended Address is placed.
+     *
+     */
+    void GenerateExtAddress(ExtAddress *aExtAddress);
+
     /**
      * This method returns a pointer to the IEEE 802.15.4 Extended Address.
      *

src/core/meshcop/joiner.cpp

@@ -508,11 +508,7 @@ void Joiner::HandleTimer(void)
     case kStateJoined:
         Mac::ExtAddress extAddress;
 
-        for (size_t i = 0; i < sizeof(extAddress); i++)
-        {
-            extAddress.m8[i] = static_cast<uint8_t>(otPlatRandomGet());
-        }
-
+        mNetif.GetMac().GenerateExtAddress(&extAddress);
         mNetif.GetMac().SetExtAddress(extAddress);
         mNetif.GetMle().UpdateLinkLocalAddress();