Fix for Multicast to level 4 (#227)

#226
- Define NETWORK_MULTICAST_ADDRESS_LEVEL_2 and NETWORK_MULTICAST_ADDRESS_LEVEL_4
- Add the above to valid addresses in `is_valid_address();`

RF24Network.cpp

@@ -43,6 +43,9 @@ volatile bool wasInterrupted;
 #endif
 uint16_t RF24NetworkHeader::next_id = 1;
 
+#define NETWORK_MULTICAST_ADDRESS_LEVEL_2 010
+#define NETWORK_MULTICAST_ADDRESS_LEVEL_4 01000
+
 #if defined(RF24_LINUX)
 /******************************************************************/
 
@@ -1094,7 +1097,7 @@ uint16_t RF24Network::direct_child_route_to(uint16_t node)
 bool RF24Network::is_valid_address(uint16_t node)
 {
     bool result = true;
-    if (node == NETWORK_MULTICAST_ADDRESS || node == 010) {
+    if (node == NETWORK_MULTICAST_ADDRESS || node == NETWORK_MULTICAST_ADDRESS_LEVEL_2 || node == NETWORK_MULTICAST_ADDRESS_LEVEL_4) {
         return result;
     }
     uint8_t count = 0;