fix: address comments

ref:

src/MeshCore.h

@@ -17,6 +17,7 @@
 #define PATH_HASH_SIZE       1
 
 #define MAX_PACKET_PAYLOAD  184
+#define MAX_GROUP_DATA_LENGTH  (MAX_PACKET_PAYLOAD - CIPHER_BLOCK_SIZE - 5)
 #define MAX_PATH_SIZE        64
 #define MAX_TRANS_UNIT      255
 
@@ -100,4 +101,4 @@ public:
   }
 };
 
-}
+}