Merge branch 'net-fix-regressions-for-generic-XDP'

Jesper Dangaard Brouer says:

====================
net: fix regressions for generic-XDP

Thanks to Brandon Cazander, who wrote a very detailed bug report that
even used perf probe's on xdp-newbies mailing list, we discovered that
generic-XDP contains some regressions when using bpf_xdp_adjust_head().

First issue were that my selftests script, that use bpf_xdp_adjust_head(),
by mistake didn't use generic-XDP any-longer. That selftest should have
caught the real regression introduced in commit 458bf2f224f0 ("net: core:
support XDP generic on stacked devices.").

To verify this patchset fix the regressions, you can invoked manually via:

  cd tools/testing/selftests/bpf/
  sudo ./test_xdp_vlan_mode_generic.sh
  sudo ./test_xdp_vlan_mode_native.sh
====================

Link: https://www.spinics.net/lists/xdp-newbies/msg01231.html
Fixes: 458bf2f224f0 ("net: core: support XDP generic on stacked devices.")
Reported by: Brandon Cazander <brandon.cazander@multapplied.net>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>