ZTS: fix removal_condense_export test case

It's been observed in the CI that the required 25% of obsolete bytes
in the mapping can be to high a threshold for this test resulting in
condensing never being triggered and a test failure.  To prevent these
failures make the existing zfs_condense_indirect_obsolete_pct tuning
available so the obsolete percentage can be reduced from 25% to 5%
during this test.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #11869

module/zfs/vdev_indirect.c

@@ -181,7 +181,7 @@ int zfs_condense_indirect_vdevs_enable = B_TRUE;
  * condenses.  Higher values will condense less often (causing less
  * i/o); lower values will reduce the mapping size more quickly.
  */
-int zfs_indirect_condense_obsolete_pct = 25;
+int zfs_condense_indirect_obsolete_pct = 25;
 
 /*
  * Condense if the obsolete space map takes up more than this amount of
@@ -446,7 +446,7 @@ vdev_indirect_should_condense(vdev_t *vd)
 	 * by the mapping.
 	 */
 	if (bytes_obsolete * 100 / bytes_mapped >=
-	    zfs_indirect_condense_obsolete_pct &&
+	    zfs_condense_indirect_obsolete_pct &&
 	    mapping_size > zfs_condense_min_mapping_bytes) {
 		zfs_dbgmsg("should condense vdev %llu because obsolete "
 		    "spacemap covers %d%% of %lluMB mapping",
@@ -1886,6 +1886,9 @@ EXPORT_SYMBOL(vdev_obsolete_sm_object);
 ZFS_MODULE_PARAM(zfs_condense, zfs_condense_, indirect_vdevs_enable, INT, ZMOD_RW,
 	"Whether to attempt condensing indirect vdev mappings");
 
+ZFS_MODULE_PARAM(zfs_condense, zfs_condense_, indirect_obsolete_pct, INT, ZMOD_RW,
+	"Minimum obsolete percent of bytes in the mapping to attempt condensing");
+
 ZFS_MODULE_PARAM(zfs_condense, zfs_condense_, min_mapping_bytes, ULONG, ZMOD_RW,
 	"Don't bother condensing if the mapping uses less than this amount of "
 	"memory");