Static inline functions for mallopt helpers

Make mallopt helper functions for each mallopt parameter so that it
can be called consistently in other areas, like setting tunables.

	* malloc/malloc.c (do_set_mallopt_check): New function.
	(do_set_mmap_threshold): Likewise.
	(do_set_mmaps_max): Likewise.
	(do_set_top_pad): Likewise.
	(do_set_perturb_byte): Likewise.
	(do_set_trim_threshold): Likewise.
	(do_set_arena_max): Likewise.
	(do_set_arena_test): Likewise.
	(__libc_mallopt): Use them.