net: ena: Flush XDP packets on error.

xdp_do_flush() should be invoked before leaving the NAPI poll function
after a XDP-redirect. This is not the case if the driver leaves via
the error path (after having a redirect in one of its previous
iterations).

Invoke xdp_do_flush() also in the error path.

Cc: Arthur Kiyanovski <akiyano@amazon.com>
Cc: David Arinzon <darinzon@amazon.com>
Cc: Noam Dagan <ndagan@amazon.com>
Cc: Saeed Bishara <saeedb@amazon.com>
Cc: Shay Agroskin <shayagr@amazon.com>
Fixes: a318c70a

 ("net: ena: introduce XDP redirect implementation")
Acked-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>