common/sfc_efx/base: fix MAE match spec class comparison API

common/sfc_efx/base: fix MAE match spec class comparison API

The helper exits once it encounters a field which hasn't its
capability status reported by the FW. Handle the corner case
when the two mask-value pairs match for the field, which, in
the absence of capability information, is sufficient to deem
the class unaffected by the field. Explain this in a comment.

Fixes: bb71f7e0a35a ("common/sfc_efx/base: add match specs class comparison API")
Cc: stable@dpdk.org
Reviewed-by: Andy Moreton <amoreton@xilinx.com>
Reviewed-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>