netdev-dpdk: Properly support non pmd threads.

netdev-dpdk: Properly support non pmd threads.

We used to reserve DPDK lcore 0 for non pmd operations, making it
difficult to use core 0 for packet processing.
DPDK 2.0 properly support non EAL threads with lcore LCORE_ID_ANY.

Using non EAL threads for non pmd threads, we do not need to reserve
any core for non pmd operations

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>