netdev-dpdk: Fix DPDK rings broken by multi queue

DPDK rings don't need one queue per PMD thread and don't support multiple
queues (set_multiq function is undefined). To fix operation with DPDK rings,
this patch ignores EOPNOTSUPP error on netdev_set_multiq() and provides, for
DPDK rings, a netdev send() function that ignores the provided queue id
(= PMD thread core id).

Suggested-by: Maryam Tahhan <maryam.tahhan@intel.com>
Signed-off-by: David Verbeiren <david.verbeiren@intel.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>