veth: take into account device reconfiguration for xdp_features flag

Take into account tx/rx queues reconfiguration setting device
xdp_features flag. Moreover consider NETIF_F_GRO flag in order to enable
ndo_xdp_xmit callback.

Fixes: 66c0e13a ("drivers: net: turn on XDP features")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>