ethdev: add queue state change event type

ethdev: add queue state change event type

This patch adds a below event type.
 - RTE_ETH_EVENT_QUEUE_STATE

This event will occur when some queues are enabled or disabled.
So far, only vhost PMD supports the event, and it indicates some queues
are enabled or disabled by virtio-net device. Such an event is needed
because virtio-net device may not enable all queues vhost PMD prepare.

Because only vhost PMD uses the event so far, it isn't an actual hardware
interrupt but a simple software event.

Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Acked-by: Rich Lane <rich.lane@bigswitch.com>
Tested-by: Rich Lane <rich.lane@bigswitch.com>
Minor modification to event name and comment:
Suggested-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>