ethdev: add flow tag

ethdev: add flow tag

A tag is a transient data which can be used during flow match. This can be
used to store match result from a previous table so that the same pattern
need not be matched again on the next table. Even if outer header is
decapsulated on the previous match, the match result can be kept.

Some device expose internal registers of its flow processing pipeline and
those registers are quite useful for stateful connection tracking as it
keeps status of flow matching. Multiple tags are supported by specifying
index.

Example testpmd commands are:

  flow create 0 ingress pattern ... / end
    actions set_tag index 2 value 0xaa00bb mask 0xffff00ff /
            set_tag index 3 value 0x123456 mask 0xffffff /
            vxlan_decap / jump group 1 / end

  flow create 0 ingress pattern ... / end
    actions set_tag index 2 value 0xcc00 mask 0xff00 /
            set_tag index 3 value 0x123456 mask 0xffffff /
            vxlan_decap / jump group 1 / end

  flow create 0 ingress group 1
    pattern tag index is 2 value spec 0xaa00bb value mask 0xffff00ff /
            eth ... / end
    actions ... jump group 2 / end

  flow create 0 ingress group 1
    pattern tag index is 2 value spec 0xcc00 value mask 0xff00 /
            tag index is 3 value spec 0x123456 value mask 0xffffff /
            eth ... / end
    actions ... / end

  flow create 0 ingress group 2
    pattern tag index is 3 value spec 0x123456 value mask 0xffffff /
            eth ... / end
    actions ... / end

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Ori Kam <orika@mellanox.com>