Fully wait for orphan inode scan to complete.

The issue with the previous attempt to fix the orphan-inodes test was
that we would regularly exceed the 120s timeout value put in there.

Instead, in this commit, we change the code to add a new counter to
indicate orphan deletion progress. When orphan inodes are deleted, the
increment of this counter indicates progress happened. Inversely,
every time the counter doesn't increment, and the orphan scan attempts
counter increments, we know that there was no more work to be done.

For safety, we wait until 2 consecutive scan attempts were made without
forward progress in the test case.

Signed-off-by: Auke Kok <auke.kok@versity.com>

kmod/src/counters.h

@@ -90,6 +90,7 @@
 	EXPAND_COUNTER(forest_read_items)			\
 	EXPAND_COUNTER(forest_roots_next_hint)			\
 	EXPAND_COUNTER(forest_set_bloom_bits)			\
+	EXPAND_COUNTER(inode_deleted)				\
 	EXPAND_COUNTER(item_cache_count_objects)		\
 	EXPAND_COUNTER(item_cache_scan_objects)			\
 	EXPAND_COUNTER(item_clear_dirty)			\

kmod/src/inode.c

@@ -1854,6 +1854,9 @@ static int try_delete_inode_items(struct super_block *sb, u64 ino)
 		goto out;
 
 	ret = delete_inode_items(sb, ino, &sinode, lock, orph_lock);
+	if (ret == 0)
+		scoutfs_inc_counter(sb, inode_deleted);
+
 out:
 	if (clear_trying)
 		clear_bit(bit_nr, ldata->trying);