common/sfc_efx/base: indicate MAE support for encapsulation

common/sfc_efx/base: indicate MAE support for encapsulation

MAE provides support for encapsulation. One needs to insert
a so-called outer rule, which can match outer packet fields,
to require that matching packets be parsed as tunnel frames
of a given type (VXLAN, Geneve, NVGRE). Then it is possible
to chain this rule with an action rule in order to match on
inner fields and carry out some actions on matching packets.

Report to clients what encapsulation types are supported by
MAE. Indicate the number of priority levels for outer rules.

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