migration: fix ram_state_pending_exact()

I removed that bit on commit:

commit c8df4a7aeffcb46020f610526eea621fa5b0cd47
Author: Juan Quintela <quintela@redhat.com>
Date:   Mon Oct 3 02:00:03 2022 +0200

    migration: Split save_live_pending() into state_pending_*

Fixes: c8df4a7aeffcb46020f610526eea621fa5b0cd47
Suggested-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/ram.c

@@ -3506,12 +3506,13 @@ static void ram_state_pending_estimate(void *opaque, uint64_t *must_precopy,
 static void ram_state_pending_exact(void *opaque, uint64_t *must_precopy,
                                     uint64_t *can_postcopy)
 {
+    MigrationState *s = migrate_get_current();
     RAMState **temp = opaque;
     RAMState *rs = *temp;
 
     uint64_t remaining_size = rs->migration_dirty_pages * TARGET_PAGE_SIZE;
 
-    if (!migration_in_postcopy()) {
+    if (!migration_in_postcopy() && remaining_size < s->threshold_size) {
         qemu_mutex_lock_iothread();
         WITH_RCU_READ_LOCK_GUARD() {
             migration_bitmap_sync_precopy(rs);