ena: Add missing statistics
Provide the following sysctl statistics in order to stay aligned with
the Linux driver:
- rx_ring.csum_good
- tx_ring.unmask_interrupt_num
Also rename the 'bad_csum' statistic name to 'csum_bad' for alignment.
Obtained from: Semihalf
MFC after: 2 weeks
Sponsored by: Amazon, Inc.