net: ena: reimplement set/get_coalesce()

1. Remove old adaptive interrupt moderation code from set/get_coalesce()
2. Add ena_update_rx_rings_intr_moderation() function for updating
   nonadaptive interrupt moderation intervals similarly to
   ena_update_tx_rings_intr_moderation().
3. Remove checks of multiple unsupported received interrupt coalescing
   parameters. This makes code cleaner and cancels the need to update
   it every time a new coalescing parameter is invented.

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>