IB/uverbs: Add support for flow tag

The struct ib_uverbs_flow_spec_action_tag associates a tag_id with the
flow defined by any number of other flow_spec entries which can reference
L2, L3, and L4 packet contents.

Use of ib_uverbs_flow_spec_action_tag allows the consumer to identify
the set of rules which where matched by
the packet by examining the tag_id in the CQE.

Signed-off-by: Moses Reuben <mosesr@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>