bnxt_en: add support for Flower based vxlan encap/decap offload

This patch adds IPv4 vxlan encap/decap action support to TC-flower
offload.

For vxlan encap, the driver maintains a tunnel encap hash-table.
When a new flow with a tunnel encap action arrives, this table
is looked up; if an encap entry exists, it uses the already
programmed encap_record_handle as the tunnel_handle in the
hwrm_cfa_flow_alloc cmd. Else, a new encap node is added and the
L2 header fields are queried via a route lookup.
hwrm_cfa_encap_record_alloc cmd is used to create a new encap
record and the encap_record_handle is used as the tunnel_handle
while adding the flow.

For vxlan decap, the driver maintains a tunnel decap hash-table.
When a new flow with a tunnel decap action arrives, this table
is looked up; if a decap entry exists, it uses the already
programmed decap_filter_handle as the tunnel_handle in the
hwrm_cfa_flow_alloc cmd. Else, a new decap node is added and
a decap_filter_handle is alloc'd via the hwrm_cfa_decap_filter_alloc
cmd. This handle is used as the tunnel_handle while adding the flow.

The code to issue the HWRM FW cmds is introduced in a follow-up patch.

Signed-off-by: Sathya Perla <sathya.perla@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>