net: mvneta: move mvneta_run_xdp after descriptors processing

Move mvneta_run_xdp routine after all descriptor processing. This is a
preliminary patch to enable multi-buffers and JUMBO frames support for
XDP

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>