IB/core: Add flow spec tunneling support

In order to support tunneling, that can be used by the QP,
both struct ib_flow_spec_tunnel and struct ib_flow_tunnel_filter can be
used to more IP or UDP based tunneling protocols (e.g NVGRE, GRE, etc).

IB_FLOW_SPEC_VXLAN_TUNNEL type flow specification is added to use this
functionality and match specific Vxlan packets.

In similar to IPv6, we check overflow of the vni value by
comparing with the maximum size.

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