sfc: insert default MAE rules to connect VFs to representors

Default rules are low-priority switching rules which the hardware uses
in the absence of higher-priority rules. Each representor requires a
corresponding rule matching traffic from its representee VF and
delivering to the PF (where a check on INGRESS_MPORT in
__ef100_rx_packet() will direct it to the representor). No rule is
required in the reverse direction, because representor TX uses a TX
override descriptor to bypass the MAE and deliver directly to the VF.
Since inserting any rule into the MAE disables the firmware's own
default rules, also insert a pair of rules to connect the PF to the
physical network port and vice-versa.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>