[FL-2053] BLE MTU processing #830

Co-authored-by: あく <alleteam@gmail.com>

applications/bt/bt_service/bt_i.h

@@ -41,6 +41,7 @@ typedef struct {
 struct Bt {
     uint8_t* bt_keys_addr_start;
     uint16_t bt_keys_size;
+    uint16_t max_packet_size;
     BtSettings bt_settings;
     BtStatus status;
     osMessageQueueId_t message_queue;