scoutfs: compact fewer srch files each time

With the introduction of incremental srch file compaction we added some
fields to the srch_compact struct to record the position of compaction
in each file.  This increased the size of the struct past the limit the
btree places on the size of item values.

We decrease the number of files per compaction from 8 to 4 to cut the
size of the srch_compcat struct in half.  This compacts twice as often,
but still relatively infrequently, and it uses half the space for srch
files waiting to hit the compaction threshold.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/format.h

@@ -371,7 +371,7 @@ struct scoutfs_srch_block {
 	 SCOUTFS_SRCH_ENTRY_MAX_BYTES)
 
 #define SCOUTFS_SRCH_LOG_BLOCK_LIMIT	(1024 * 1024 / SCOUTFS_BLOCK_LG_SIZE)
-#define SCOUTFS_SRCH_COMPACT_ORDER	3
+#define SCOUTFS_SRCH_COMPACT_ORDER	2
 #define SCOUTFS_SRCH_COMPACT_NR		(1 << SCOUTFS_SRCH_COMPACT_ORDER)
 
 /*