net: mvneta: do not redirect frames during reconfiguration

Disable frames injection in mvneta_xdp_xmit routine during hw
re-configuration in order to avoid hardware hangs

Fixes: b0a43db9

 ("net: mvneta: add XDP_TX support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>