virtio only support packed ring size power of 2

Issue discription：
When QEMU starts with "-device virtio-net-pci,netdev=netdev0,mac=52:54:00:00:00:01,disable-modern=false,mrg_rxbuf=on,rx_queue_size=1025,tx_queue_size=1025,mq=on,vectors=15,packed=on"

It raises error: Invalid rx_queue_size (= 1025), must be a power of 2 between 256 and 1024

Analysis:
According to virtio1.1 spec, the packed queue size value does not have to be a power of 2.