sfc: add offloading of 'foreign' TC (decap) rules

A 'foreign' rule is one for which the net_dev is not the sfc netdevice
 or any of its representors.  The driver registers indirect flow blocks
 for tunnel netdevs so that it can offload decap rules.  For example:

    tc filter add dev vxlan0 parent ffff: protocol ipv4 flower \
        enc_src_ip 10.1.0.2 enc_dst_ip 10.1.0.1 \
        enc_key_id 1000 enc_dst_port 4789 \
        action tunnel_key unset \
        action mirred egress redirect dev $REPRESENTOR

When notified of a rule like this, register an encap match on the IP
 and dport tuple (creating an Outer Rule table entry) and insert an MAE
 action rule to perform the decapsulation and deliver to the representee.

Moved efx_tc_delete_rule() below efx_tc_flower_release_encap_match() to
 avoid the need for a forward declaration.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>