i40evf: fix RSS with less Rx queues than Tx queues

i40evf: fix RSS with less Rx queues than Tx queues

I40e VF driver uses the num_queue_pairs in vf structure to construct
queue index look up table. When the nb_rx_queue is less than nb_tx_queue,
num_queue_pairs is equal to nb_tx_queue. It will make the table use
invalid queue index, then application cannot poll packets on these queues.

This patch also moves the inline function i40e_align_floor from
i40e_ethdev.c to i40e_ethdev.h.

Test report: http://dpdk.org/ml/archives/dev/2015-July/021838.html

Signed-off-by: Jingjing Wu <jingjing.wu@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>
Tested-by: Qian Xu <qian.q.xu@intel.com>