selftests: net: tc_taprio: new test

Add a forwarding path test for tc-taprio, based on isochron. This is
specifically intended for NICs with an offloaded data path (switchdev/DSA)
and requires taprio 'flags 2'. Also, $h1 and $h2 must support hardware
timestamping, and $h1 tc-etf offload, for isochron to work.

Packets received by a switch while the egress port has a taprio schedule
with an open gate for the traffic class must be sent right away.

Packets received by the switch while the traffic class gate must be
delayed until it opens.

Packets received by the switch must be dropped if the gate for the
traffic class never opens.

Packets should pass if the maximum SDU for the traffic class allows it,
and should be dropped otherwise.

The schedule should auto-update itself if clock jumps take place while
taprio is installed. Repeat most of the above tests after forcing two
clock jumps, one backwards (in Jan 1970) and one back into the present.

Symlink it from tools/testing/selftests/drivers/net/dsa, because usually
DSA ports have the same MAC address, and we need STABLE_MAC_ADDRS=yes
from its forwarding.config for the test to run successfully.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20250426144859.3128352-5-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: vladimiroltean

tools/testing/selftests/drivers/net/dsa/tc_taprio.sh

@@ -0,0 +1 @@
+run_net_forwarding_test.sh