selftests: team: add non-Ethernet header_ops reproducer

selftests: team: add non-Ethernet header_ops reproducer

Add a team selftest that sets up:
  g0 (gre) -> b0 (bond) -> t0 (team)

and triggers IPv6 traffic on t0. This reproduces the non-Ethernet
header_ops confusion scenario and protects against regressions in stacked
team/bond/gre configurations.

Using this script, the panic reported by syzkaller can be reproduced [1].

After the fix:

  # ./non_ether_header_ops.sh
  PASS: non-Ethernet header_ops stacking did not crash

[1] https://syzkaller.appspot.com/bug?extid=3d8bc31c45e11450f24c

Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Link: https://patch.msgid.link/20260320072139.134249-3-jiayuan.chen@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>