limit crawls for metadumper

LRU crawler metadumper is used for getting snapshot-y looks at the LRU's.
Since there's no default limit, it'll get any new items added or bumped since
the roll started.

with this change it limits the number of items dumped to the number that
existed in that LRU when the roll was kicked off. You still end up with an
approximation, but not a terrible one:

- items bumped after the crawler passes them likely won't be revisited
- items bumped before the crawler passes them will likely be visited toward
  the end, or mixed with new items.
- deletes are somewhere in the middle.

1 files changed, 1 insertions, 0 deletions

diff --git a/items.h b/items.h
index bf126d7..3b99c66 100644
--- a/items.h
+++ b/items.h
@@ -25,6 +25,7 @@ void do_item_update_nolock(item *it);
 int  do_item_replace(item *it, item *new_it, const uint32_t hv);
 
 int item_is_flushed(item *it);
+unsigned int do_get_lru_size(uint32_t id);
 
 void do_item_linktail_q(item *it);
 void do_item_unlinktail_q(item *it);