migration: Add multifd capability

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>

--

Use new DEFINE_PROP
diff --git a/migration/migration.h b/migration/migration.h
index 1881e4a..b7437f1 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -174,6 +174,7 @@
 bool migrate_zero_blocks(void);
 
 bool migrate_auto_converge(void);
+bool migrate_use_multifd(void);
 
 int migrate_use_xbzrle(void);
 int64_t migrate_xbzrle_cache_size(void);