net: dpaa2-eth: do not always set xsk support in xdp_features flag

Do not always add NETDEV_XDP_ACT_XSK_ZEROCOPY bit in xdp_features flag
but check if the NIC really supports it.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Link: https://lore.kernel.org/r/3dba6ea42dc343a9f2d7d1a6a6a6c173235e1ebf.1676471386.git.lorenzo@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>