selftests: forwarding: Fix test for different devices

selftests: forwarding: Fix test for different devices

When running the test on the Spectrum ASIC the generated packets are
counted on the ingress filter and injected back to the pipeline because
of the 'pass' action. The router block then drops the packets due to
checksum error, as the test generates packets with zero checksum.

When running the test on an emulator that is not as strict about
checksum errors the test fails since packets are counted twice. Once by
the emulated ASIC on its ingress filter and again by the kernel as the
emulator does not perform checksum validation and allows the packets to
be trapped by a matching host route.

Fix this by changing the action to 'drop', which will prevent the packet
from continuing further in the pipeline to the router block.

For veth pairs this change is essentially a NOP given packets are only
processed once (by the kernel).

Fixes: 6e32157f3984 ("selftests: forwarding: vxlan_bridge_1d: Add an ECN decap test")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>