Copter: support `DO_RETURN_PATH_START` in AUTO RTL mode #12099

Job	Run time
build (check_autotest_options)	1m 31s
build (param_parse)	51s
build (python-cleanliness)	54s
build (astyle-cleanliness)	38s
build (validate_board_list)	1m 5s
	4m 59s

Provide feedback