net/virtio: allocate queue at init stage

net/virtio: allocate queue at init stage

Queue allocation should be done once, since the queue related info (such
as vring addreess) will only be informed to the vhost-user backend once
without virtio device reset.

That means, if you allocate queues again after the vhost-user negotiation,
the vhost-user backend will not be informed any more. Leading to a state
that the vring info mismatches between virtio PMD driver and vhost-backend:
the driver switches to the new address has just been allocated, while the
vhost-backend still sticks to the old address has been assigned in the init
stage.

Unfortunately, that is exactly how the virtio driver is coded so far: queue
allocation is done at queue_setup stage (when rte_eth_tx/rx_queue_setup is
invoked). This is wrong, because queue_setup can be invoked several times.
For example,

    $ start_testpmd.sh ... --txq=1 --rxq=1 ...
    > port stop 0
    > port config all txq 1 # just trigger the queue_setup callback again
    > port config all rxq 1
    > port start 0

The right way to do is allocate the queues in the init stage, so that the
vring info could be persistent with the vhost-user backend.

Besides that, we should allocate max_queue pairs the device supports, but
not nr queue pairs firstly configured, to make following case work.

    $ start_testpmd.sh ... --txq=1 --rxq=1 ...
    > port stop 0
    > port config all txq 2
    > port config all rxq 2
    > port start 0

Since the allocation is switched to init stage, the free should also
moved from the rx/tx_queue_release to dev close stage. That leading we
could do nothing an empty rx/tx_queue_release() implementation.

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>