Add the "stats.arenas.<i>.lg_dirty_mult" mallctl.

include/jemalloc/internal/ctl.h

@@ -34,6 +34,7 @@ struct ctl_arena_stats_s {
 	bool			initialized;
 	unsigned		nthreads;
 	const char		*dss;
+	ssize_t			lg_dirty_mult;
 	size_t			pactive;
 	size_t			pdirty;
 	arena_stats_t		astats;