net: atm: pppoatm: use new API for wakeup tasklet

This converts the driver to use the new tasklet API introduced in
commit 12cc923f ("tasklet: Introduce new initialization API")

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Link: https://lore.kernel.org/r/20210127173256.13954-2-kernel@esmil.dk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>