selftests/bpf: fix xdp_redirect xdp-features selftest for veth driver

xdp-features supported by veth driver are no more static, but they
depends on veth configuration (e.g. if GRO is enabled/disabled or
TX/RX queue configuration). Take it into account in xdp_redirect
xdp-features selftest for veth driver.

Fixes: fccca038 ("veth: take into account device reconfiguration for xdp_features flag")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/bc35455cfbb1d4f7f52536955ded81ad47d8dc54.1680777371.git.lorenzo@kernel.org


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>