Move Rx/Tx routines to separate file.
Some functions:
- ena_restore_device,
- ena_destroy_device,
- ena_up,
- ena_down,
- ena_refill_rx_bufs
could be reused in upcoming netmap code in the driver. To make it
possible, they were moved to ena.h header.
Submitted by: Rafal Kozik <rk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.