eventdev: add event type for eth Rx adapter

eventdev: add event type for eth Rx adapter

Add RTE_EVENT_TYPE_ETH_RX_ADAPTER event type. Certain platforms (e.g.,
octeontx), in the event dequeue function, need to identify events
injected from ethernet hardware into eventdev so that DPDK mbuf can be
populated from the HW descriptor.

Events injected from ethernet hardware would use an event type of
RTE_EVENT_TYPE_ETHDEV and events injected from the rx adapter service
function would use an event type of RTE_EVENT_TYPE_ETH_RX_ADAPTER to
help the event dequeue function differentiate between these two event
sources.

Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>