tc/cls_flower: Classify packet in ip tunnels

tc/cls_flower: Classify packet in ip tunnels

Introduce classifying by metadata extracted by the tunnel device.
Outer header fields - source/dest ip and tunnel id, are extracted from
the metadata when classifying.

For example, the following will add a filter on the ingress Qdisc of shared
vxlan device named 'vxlan0'. To forward packets with outer src ip
11.11.0.2, dst ip 11.11.0.1 and tunnel id 11. The packets will be
forwarded to tap device 'vnet0':

$ tc filter add dev vxlan0 protocol ip parent ffff: \
    flower \
      enc_src_ip 11.11.0.2 \
      enc_dst_ip 11.11.0.1 \
      enc_key_id 11 \
      dst_ip 11.11.11.1 \
    action mirred egress redirect dev vnet0

Signed-off-by: Amir Vadai <amir@vadai.me>