selftests: drv-net: add a simple TSO test

selftests: drv-net: add a simple TSO test

Add a simple test for TSO. Send a few MB of data and check device
stats to verify that the device was performing segmentation.
Do the same thing over a few tunnel types.

Injecting GSO packets directly would give us more ability to test
corner cases, but perhaps starting simple is good enough?

  # ./ksft-net-drv/drivers/net/hw/tso.py
  # Detected qstat for LSO wire-packets
  KTAP version 1
  1..14
  ok 1 tso.ipv4 # SKIP Test requires IPv4 connectivity
  ok 2 tso.vxlan4_ipv4 # SKIP Test requires IPv4 connectivity
  ok 3 tso.vxlan6_ipv4 # SKIP Test requires IPv4 connectivity
  ok 4 tso.vxlan_csum4_ipv4 # SKIP Test requires IPv4 connectivity
  ok 5 tso.vxlan_csum6_ipv4 # SKIP Test requires IPv4 connectivity
  ok 6 tso.gre4_ipv4 # SKIP Test requires IPv4 connectivity
  ok 7 tso.gre6_ipv4 # SKIP Test requires IPv4 connectivity
  ok 8 tso.ipv6
  ok 9 tso.vxlan4_ipv6
  ok 10 tso.vxlan6_ipv6
  ok 11 tso.vxlan_csum4_ipv6
  ok 12 tso.vxlan_csum6_ipv6
  # Testing with mangleid enabled
  ok 13 tso.gre4_ipv6
  ok 14 tso.gre6_ipv6
  # Totals: pass:7 fail:0 xfail:0 xpass:0 skip:7 error:0

Note that the test currently depends on the driver reporting
the LSO count via qstat, which appears to be relatively rare
(virtio, cisco/enic, sfc/efc; but virtio needs host support).

Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250218225426.77726-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>