efi_loader: fix efi_net_get_status

The returned interrupt status was wrong.

As out transmit buffer is empty we need to always set
EFI_SIMPLE_NETWORK_TRANSMIT_INTERRUPT.

When we have received a packet we need to set
EFI_SIMPLE_NETWORK_RECEIVE_INTERRUPT.

Furthermore we should call efi_timer_check() to handle events.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Alexander Graf <agraf@suse.de>