default to jemalloc when both hardened_malloc and jemalloc enabled.

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/alloc/je.rs

@@ -1,3 +1,5 @@
+//! jemalloc allocator
+
 use std::ffi::{c_char, c_void};
 
 use tikv_jemalloc_ctl as mallctl;