Ensure that if the interrupt handler is entered then only try and do tx
work if the tx irq is enabled.
Signed-off-by: NBen Dooks <ben.dooks@codethink.co.uk>
Tested-by: NCarlo Caione <carlo@endlessm.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>