migration: move income process out of multifd

Move the call to migration_incoming_process() out of multifd code.  It's
a bit strange that we can migration generic calls in multifd code.
Instead, let multifd_recv_new_channel() return a boolean showing whether
it's ready to continue the incoming migration.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180627132246.5576-3-peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/migration/migration.c b/migration/migration.c
index 94d71f8..aea6fb7 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -507,7 +507,10 @@
         migration_incoming_setup(f);
         return;
     }
-    multifd_recv_new_channel(ioc);
+
+    if (multifd_recv_new_channel(ioc)) {
+        migration_incoming_process();
+    }
 }
 
 /**