net/sfc: multiply of specs with an unknown EtherType

net/sfc: multiply of specs with an unknown EtherType

Hardware filter specification for encapsulated traffic must contain
EtherType. In terms of RTE flow API, this would require L3 item to be
used in the flow rule. In the simplest case, if the user needs to filter
encapsulated traffic without knowledge of exact EtherType, they will
have to create multiple variants of the flow rule featuring all possible
L3 items (IPv4, IPv6), respectively. In order to hide the gory details
and avoid such a complication, this patch implements a mechanism to
auto-complete the filter specifications if need be.

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>