net/mlx5e: Add support for hw encapsulation of MPLS over UDP

MPLS over UDP is supported by adding a rule on a representor net device
which does tunnel_key set, push mpls and forward to a baredup device. At
the hardware level we use a packet_reformat_context object to do the
encapsulation of the packet.

The resulting packet looks as follows (left side transmitted first):
outer L2 | outer IP | UDP | MPLS | inner L3 and data |

Example usage:
  tc filter add dev $rep0 protocol ip prio 1 root flower skip_sw  \
     action tunnel_key set src_ip 8.8.8.21 dst_ip 8.8.8.24 id 555 \
     dst_port 6635 tos 4 ttl 6 csum action mpls push protocol 0x8847 \
     label 555 tc 3 action mirred egress redirect dev bareudp0

This is how the filter is shown with tc filter show:
tc filter show dev enp59s0f0_0 ingress
filter protocol ip pref 1 flower chain 0
filter protocol ip pref 1 flower chain 0 handle 0x1
  eth_type ipv4
  skip_sw
  in_hw in_hw_count 1
        action order 1: tunnel_key  set
        src_ip 8.8.8.21
        dst_ip 8.8.8.24
        key_id 555
        dst_port 6635
        csum
        tos 0x4
        ttl 6 pipe
         index 1 ref 1 bind 1

        action order 2: mpls  push protocol mpls_uc label 555 tc 3 ttl 255 pipe
         index 1 ref 1 bind 1

        action order 3: mirred (Egress Redirect to device bareudp0) stolen
        index 1 ref 1 bind 1

Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Eli Britstein <elibr@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>