mlx4: fix XDP_TX is acting like XDP_PASS on TX ring full

The XDP_TX action can fail transmitting the frame in case the TX ring
is full or port is down.  In case of TX failure it should drop the
frame, and not as now call 'break' which is the same as XDP_PASS.

Fixes: 9ecc2d86

 ("net/mlx4_en: add xdp forwarding and data write support")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Brenden Blanco <bblanco@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>