dpdk: enable RX interrupts for the virtio driver

dpdk: enable RX interrupts for the virtio driver

Type: improvement

Request use of RX interrupts for virtio if the system will support it,
which is done by applying the same check as in the virtio driver,
namely whether multiple interrupts are supported. This allows the use
of RX adaptive/interrupt mode instead of just polling, which is useful
in virtualised environments where functionality may be more important
than performance and so using polling mode is wasteful.

Signed-off-by: Robert Shearman <robertshearman@gmail.com>
Change-Id: I29527b6f04b0b1d0c9f9424751b2bd252ed10505