libertas: go back to ps mode without commands pending

Removes the old todo block and checks only whether ieee powersave
mode is requested. We still have to check for being connected as
this powersave mode includes logic for regularly waking up and
checking for packets which only makes sense when connected.
For not being connected, another mode is needed.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>