vmm: api: Make VmSendMigrationData.local optional

Fixes: #3756

Signed-off-by: Feng Ye <yefeng@smartx.com>

vmm/src/api/mod.rs

@@ -196,6 +196,7 @@ pub struct VmSendMigrationData {
     /// URL to migrate the VM to
     pub destination_url: String,
     /// Send memory across socket without copying
+    #[serde(default)]
     pub local: bool,
 }