qm: multiqueue specify that it needs to be vCPUs not cores

qm: multiqueue specify that it needs to be vCPUs not cores

total number of cores != vCPUs if there is more than one socket
configured. according to the redhat docs it should be vCPUs not cores:

> Multi-queue virtio-net provides the greatest performance benefit when:
> [..]
> - The number of queues is equal to the number of vCPUs.

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_tuning_and_optimization_guide/sect-virtualization_tuning_optimization_guide-networking-techniques#sect-Virtualization_Tuning_Optimization_Guide-Networking-Multi-queue_virtio-net
Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>