Refactor bridge packet handling to use common magic number and size constants

variants/lilygo_tlora_v2_1/platformio.ini

@@ -198,7 +198,7 @@ build_flags =
   -D MAX_NEIGHBOURS=8
   -D WITH_ESPNOW_BRIDGE=1
   -D WITH_ESPNOW_BRIDGE_SECRET='"shared-secret"'
-;  -D MESH_PACKET_LOGGING=1
+  -D MESH_PACKET_LOGGING=1
 ;  -D MESH_DEBUG=1
 ;  -D CORE_DEBUG_LEVEL=3
 lib_deps =