framework/st_things : Reduce KEY_MANAGER_MAX_DATA_LENGTH.
1. Reduce KEY_MANAGER_MAX_DATA_LENGTH from 200 to 21.
2. The string's length of 21 is sufficient to convert long long integer into string.
#define FIRMWARE_PROPERTY_VENDER "vender"
#define FIRMWARE_PROPERTY_MODEL "model"
-#define KEY_MANAGER_MAX_DATA_LENGTH 200
+#define KEY_MANAGER_MAX_DATA_LENGTH 21
#define KEY_MANAGER_INT_DEFAULT_DATA "0"
#define KEY_MANAGER_STR_DEFAULT_DATA " "
#define KEY_MANAGER_BOL_DEFAULT_DATA "0"
