We refer to TC NIC rule that involves forwarding as "hairpin".

All hairpin rules from the current NIC device (called "func" in
the code) to a given NIC device ("peer") are steered into the
same hairpin RQ/SQ pair.

The hairpin pair is set on demand and removed when there are no
TC rules that need it.

Here's a TC rule that matches on icmp, does header re-write of the
dst mac and hairpin from RX/enp1s2f1 to TX/enp1s2f2 (enp1s2f1/2 are
two mlx5 devices):

tc filter add dev enp1s2f1 protocol ip parent ffff: prio 2
    flower skip_sw ip_proto icmp
     action pedit ex munge eth dst set 10:22:33:44:55:66 pipe
     action mirred egress redirect dev enp1s2f2
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>