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>