sfc: ef10: implement ethtool::get_fec_stats

Report what appears to be the standard block counts:
 - 30.5.1.1.17 aFECCorrectedBlocks
 - 30.5.1.1.18 aFECUncorrectableBlocks

Don't report the per-lane symbol counts, if those really
count symbols they are not what the standard calls for
(even if symbols seem like the most useful thing to count.)

Fingers crossed that fec_corrected_errors is not in symbols.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>