libceph, crush: per-pool crush_choose_arg_map for crush_do_rule()

If there is no crush_choose_arg_map for a given pool, a NULL pointer is
passed to preserve existing crush_do_rule() behavior.

Reflects ceph.git commits 55fb91d64071552ea1bc65ab4ea84d3c8b73ab4b,
                          dbe36e08be00c6519a8c89718dd47b0219c20516.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

net/ceph/crush/crush.c

@@ -1,6 +1,7 @@
 #ifdef __KERNEL__
 # include <linux/slab.h>
 # include <linux/crush/crush.h>
+void clear_choose_args(struct crush_map *c);
 #else
 # include "crush_compat.h"
 # include "crush.h"
@@ -127,6 +128,8 @@ void crush_destroy(struct crush_map *map)
 
 #ifndef __KERNEL__
 	kfree(map->choose_tries);
+#else
+	clear_choose_args(map);
 #endif
 	kfree(map);
 }