virtio: Extend vhost multi-queues support beyond 8 queue pairs

virtio: Extend vhost multi-queues support beyond 8 queue pairs

Current vhost multi-queues support has a hard limit of 8 queue pairs
due to static vring array. This limit was raised in qemu. VPP should
support more than 8 queue pairs also.

Change static vring allocation to dynamic. When the interface is
created, we allocate 8 queue pairs to begin with. We also keep track
of how many queue pairs that the interface actually uses.
We reply VHOST_USER_GET_QUEUE_NUM with 128 as our maximum number of
support queue pair. When qemu starts initializing queue pair greater
than 8, we expand the vrings as needed on demand.

Type: improvement

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: I4a02d987d52d1bbe601b00e71f650fe6ebfcc0d7