netdev-dpdk: Increase tx queue size and rx batch size

These values has been found to give the best throughput
in simple cases (1 flow 64 bytes UDP packets).

Signed-off-by: Daniele Di Proietto <ddiproietto@vmware.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
dpif-netdev: Reduce netdev_flow_key size

struct 'miniflow' already contains MINI_N_INLINE values, therefore
we can save few bytes in netdev_flow_key.

Signed-off-by: Daniele Di Proietto <ddiproietto@vmware.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>