[PATCH] examples/distributor: one Tx queue is enough

[Tu, Lijuan]

> Do we know why DTS is making this change? Does having more TX queues than
> necessary cause problems?

DTS is to reduce tx queues to enable many workers for performance testing.
Distributor application creates one Tx queue per core, and total (lcore-1) queues, 
Which make it only 1 worker, but it only use a single queue to transmit. 
That's not make sense, so we request to fix it.