dpif-netdev: Create multiple tx/rx queues when adding dpdk interface.

dpif-netdev: Create multiple tx/rx queues when adding dpdk interface.

Before this commit, ovs creates one tx and one rx queue for
each dpdk interface and uses only one poll thread for handling
I/O of all dpdk interfaces.  An upcoming patch will allow multiple
poll threads be created.  As a preparation, this commit changes
the dpif-netdev to create multiple tx/rx queues when the dpdk
interface is added.

Specifically, the number of rx queues will still be one per-dpdk
interface for this commit.  But upcoming work will allow user
create multiple rx queues.  The number of tx queues will be the
number of cpu cores on the machine.  Although not all the tx queues
will be used, each poll thread will have its own queue for
transmission on the dpdk interface.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>