common/sfc_efx/base: add match specs class comparison API

common/sfc_efx/base: add match specs class comparison API

From MAE standpoint, a flow rule belongs to some class. Field capabilities
advertised by the FW provide a hint on whether changing a particular match
field value or its mask will affect the class of the rule. A client driver
can make use of the concept of a class by comparing a rule being validated
with already inserted ones so that if an existing rule with the same class
is encountered, it will become possible to skip making an explicit request
to the FW because the class of an already inserted rule is wittingly valid.

Implement an API for client drivers to carry out the said class comparison.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>