migration: Move more initializations to migrate_init()

Initialization of mig_stats, compression_counters and VFIO bytes
transferred is hard-coded in migration code path and snapshot code path.

Make the code cleaner by initializing them in migrate_init().

Suggested-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

migration/savevm.c

@@ -1620,9 +1620,6 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
     }
 
     migrate_init(ms);
-    memset(&mig_stats, 0, sizeof(mig_stats));
-    memset(&compression_counters, 0, sizeof(compression_counters));
-    migration_reset_vfio_bytes_transferred();
     ms->to_dst_file = f;
 
     qemu_mutex_unlock_iothread();