migration: Add postcopy_preempt_active()

Add the helper to show that postcopy preempt enabled, meanwhile active.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/migration/ram.c b/migration/ram.c
index cc72c24..00a2e30 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -162,6 +162,11 @@
     return ret;
 }
 
+static bool postcopy_preempt_active(void)
+{
+    return migrate_postcopy_preempt() && migration_in_postcopy();
+}
+
 bool ramblock_is_ignored(RAMBlock *block)
 {
     return !qemu_ram_is_migratable(block) ||
@@ -2433,7 +2438,7 @@
 /* We need to make sure rs->f always points to the default channel elsewhere */
 static void postcopy_preempt_reset_channel(RAMState *rs)
 {
-    if (migrate_postcopy_preempt() && migration_in_postcopy()) {
+    if (postcopy_preempt_active()) {
         rs->postcopy_channel = RAM_CHANNEL_PRECOPY;
         rs->f = migrate_get_current()->to_dst_file;
         trace_postcopy_preempt_reset_channel();
@@ -2471,7 +2476,7 @@
         return 0;
     }
 
-    if (migrate_postcopy_preempt() && migration_in_postcopy()) {
+    if (postcopy_preempt_active()) {
         postcopy_preempt_choose_channel(rs, pss);
     }