netdev-dpdk: Obtain number of queues for vhost ports from attached virtio.

netdev-dpdk: Obtain number of queues for vhost ports from attached virtio.

Currently, there are few inconsistencies in ways to configure number of
queues for netdev device:

	* dpif-netdev can't know about exact number of queues
	  allocated inside netdev.
	  This leads to constant mapping of queue-ids to 'real' ones.

	* We are able to configure 'n_rxq' for vhost-user devices, but
	  there is only one sane number of rx queues which must be used
	  and configured manually (number of queues that allocated
	  in QEMU).

This patch disables configuration of 'n_rxq' for DPDK vHost devices.
Configuration of rx and tx queues now automatically applied from
connected virtio device. Standard reconfiguration mechanism was used to
apply this changes.

Also, now 'n_txq' and 'n_rxq' are always the real numbers of queues
in the device.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>