[mac-types] add Mac::ExtendedPanId::Clear() method (#4315)

src/core/mac/mac.cpp

@@ -122,7 +122,7 @@ Mac::Mac(Instance &aInstance)
 
     mCcaSuccessRateTracker.Reset();
     memset(&mCounters, 0, sizeof(otMacCounters));
-    memset(&mExtendedPanId, 0, sizeof(ExtendedPanId));
+    mExtendedPanId.Clear();
 
     mSubMac.Enable();
 

src/core/mac/mac_types.hpp

@@ -461,6 +461,12 @@ public:
      */
     typedef String<kInfoStringSize> InfoString;
 
+    /**
+     * This method clears the Extended PAN Identifier (sets all bytes to zero).
+     *
+     */
+    void Clear(void) { memset(this, 0, sizeof(*this)); }
+
     /**
      * This method evaluates whether or not the Extended PAN Identifiers match.
      *