vmm: extract a helper to send the VM config

This further decreases boilerplate code in lib.rs while keeping the
behavior.

On-behalf-of: SAP sebastian.eydam@sap.com
Signed-off-by: Sebastian Eydam <sebastian.eydam@cyberus-technology.de>

vmm/src/lib.rs

@@ -1434,15 +1434,7 @@ impl Vmm {
             common_cpuid,
             memory_manager_data: vm.memory_manager_data(),
         };
-        let config_data = serde_json::to_vec(&vm_migration_config).unwrap();
-        Request::config(config_data.len() as u64).write_to(&mut socket)?;
-        socket
-            .write_all(&config_data)
-            .map_err(MigratableError::MigrateSocket)?;
-        migration_transport::expect_ok_response(
-            &mut socket,
-            MigratableError::MigrateSend(anyhow!("Error during config migration")),
-        )?;
+        migration_transport::send_config(&mut socket, &vm_migration_config)?;
 
         // Let every Migratable object know about the migration being started.
         vm.start_migration()?;