try_to_free_nats() is usually called with parameter nr_shrink as
	"nm_i->nat_cnt - NM_WOUT_THRESHOLD"
by flush_nat_entries() during checkpointing process.
However, this is inconsistent with the actual threshold check as
	"if (nm_i->nat_cnt < 2 * NM_WOUT_THRESHOLD)"
, which will ignore the free_nats requests when
	NM_WOUT_THRESHOLD < nm_i->nat_cnt < 2 * NM_WOUT_THRESHOLD
So fix the threshold check condition.
Signed-off-by: Haicheng Li <haicheng.li@linux.intel.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
 {
        struct f2fs_nm_info *nm_i = NM_I(sbi);
 
-       if (nm_i->nat_cnt < 2 * NM_WOUT_THRESHOLD)
+       if (nm_i->nat_cnt <= NM_WOUT_THRESHOLD)
                return 0;
 
        write_lock(&nm_i->nat_tree_lock);