net/sfc: multiply of specs with an unknown destination MAC

net/sfc: multiply of specs with an unknown destination MAC

To filter all traffic, need to create two hardware filter specifications
with both unknown unicast and unknown multicast destination MAC address
match flags.

In terms of RTE flow API, this would require adding multiple flow rules
with corresponding ETH items. In order to avoid such a complication, the
patch implements a mechanism to auto-complete an underlying filter
representation of a flow rule in order to create additional filter
specifications featuring the missing match flags.

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>