ddt: reduce DDT_NAMELEN

This is the buffer size passed to ddt_object_name(), to expand the
DMU_POOL_DDT format. That format inserts the table checksum, class and
type names, which as I write this are max 6, 9 and 3, respectively.

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Sponsored-by: https://despairlabs.com/sponsor/
Closes openzfs#15908

include/sys/ddt_impl.h

@@ -66,7 +66,12 @@ extern void ddt_stat_update(ddt_t *ddt, ddt_entry_t *dde, uint64_t neg);
  * outside of the DDT implementation proper, and if you do, consider moving
  * them up.
  */
-#define	DDT_NAMELEN	110
+
+/*
+ * Enough room to expand DMU_POOL_DDT format for all possible DDT
+ * checksum/class/type combinations.
+ */
+#define	DDT_NAMELEN	32
 
 extern uint64_t ddt_phys_total_refcnt(const ddt_entry_t *dde);