Support having multiple virtif-based drivers in one kernel.
Support having multiple virtif-based drivers in one kernel.

Avoid having different 'if_virt' modules shadow each other,
by giving each module a unique name based on their VIRTIF_BASE.

Sync'ed with pooka's upstream change (1.48).

jqyy/drv-netif-dpdk,jqyy/drv-netif-dpdk