ethdev: add packet count parameter to Rx callback

ethdev: add packet count parameter to Rx callback

Added a parameter to the RX callback to pass in the number of
available RX packets in addition to the number of dequeued packets.
This provides the RX callback functions with additional information
that can be used to decide how packets from a burst are handled.

The TX callback doesn't require this additional parameter so the RX
and TX callbacks no longer have the same function parameters. As such
the single RX/TX callback has been refactored into two separate callbacks.

Signed-off-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>