dpif-netdev: fix race for queues between pmd threads.

dpif-netdev: fix race for queues between pmd threads.

Currently pmd threads select queues in pmd_load_queues() according to
get_n_pmd_threads_on_numa(). This behavior leads to race between pmds,
beacause dp_netdev_set_pmds_on_numa() starts them one by one and
current number of threads changes incrementally.

As a result we may have the following situation with 2 pmd threads:

* dp_netdev_set_pmds_on_numa()
* pmd12 thread started. Currently only 1 pmd thread exists.
dpif_netdev(pmd12)|INFO|Core 1 processing port 'port_1'
dpif_netdev(pmd12)|INFO|Core 1 processing port 'port_2'
* pmd14 thread started. 2 pmd threads exists.
dpif_netdev|INFO|Created 2 pmd threads on numa node 0
dpif_netdev(pmd14)|INFO|Core 2 processing port 'port_2'

We have:
core 1 --> port 1, port 2
core 2 --> port 2

Fix this by starting pmd threads only after all of them have
been configured.

Cc: Daniele Di Proietto <diproiettod at vmware.com>
Cc: Dyasly Sergey <s.dyasly at samsung.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: Daniele Di Proietto <diproiettod@vmware.com>
Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
Signed-off-by: Ethan Jackson <ethan@nicira.com>