net: stmmac: add missing NETDEV_XDP_ACT_XSK_ZEROCOPY bit to xdp_features

Add missing xsk zero-copy bit to xdp_features capability flag.

Fixes: 66c0e13a ("drivers: net: turn on XDP features")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/c8949baafdf617188dcedb9033ce5a9ca6e9e5ff.1676195440.git.lorenzo@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>