Suspend feature for multiple devices of same type in bhyve

The FreeBSD specific hypervisor solution, bhyve, is a mature virtualization solution that allows its users to configure the virtual machines in a robust manner by adding different types of devices. Moreover, the virtual machine state can be suspended for a later use by using the snapshotting mechanism. However, the existing snapshot mechanism can only store the state of one device of each type. This behaviour may be troublesome for entities that want to use the save and restore mechanism for virtual machines with multiple same type devices (e.g., two disks, two network interfaces) since it can lead to an inconsistent virtual machine state. This paper proposes a solution for extending this feature by allowing the saving and restoration of multiple devices of the same type, whenever they are used together