[mac] add reserved value to source address parsing (#8326)

Fails packet parsing if the reserved value is found in the source
addressing field instead of marking the address as "none".

src/core/mac/mac_frame.cpp

@@ -378,9 +378,14 @@ Error Frame::GetSrcAddr(Address &aAddress) const
         aAddress.SetExtended(&mPsdu[index], ExtAddress::kReverseByteOrder);
         break;
 
-    default:
+    case kFcfSrcAddrNone:
         aAddress.SetNone();
         break;
+
+    default:
+        // reserved value
+        error = kErrorParse;
+        break;
     }
 
 exit: