net/sfc: avoid creation of ineffective flow rules

net/sfc: avoid creation of ineffective flow rules

Despite being versatile, the hardware support for filtering has a number
of special properties which must be taken into account. Namely, there is
a known set of valid filters which don't take any effect despite being
accepted by the hardware.

The combinations of match flags and field values which can describe the
exceptional filters are as follows:
- ETHER_TYPE or ETHER_TYPE | LOC_MAC with IPv4 or IPv6 EtherType
- ETHER_TYPE | IP_PROTO or ETHER_TYPE | IP_PROTO | LOC_MAC with UDP or
TCP IP protocol value
- The same combinations with OUTER_VID and/or INNER_VID

These exceptional filters can be expressed in terms of RTE flow rules.
If the user creates such a flow rule, no traffic will hit the underlying
filter, and no errors will be reported.

This patch adds a means to prevent such ineffective flow rules from
being created.

Signed-off-by: Roman Zhukov <roman.zhukov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Ivan Malov <ivan.malov@oktetlabs.ru>