Sierra modems are not powered down when mobile broadband is disabled

[Marius B. Kotsbak]

When mobile broadband is disabled, Sierra modems are not turned off (set in low power mode, CFUN=4).

Fixed upstream MM master/0.7, and by the following commits in to 0.6 branch:

commit 2df73f4db46590e7dfefcb5e1a6712b2ee5d12c0
Author: Marius B. Kotsbak <email address hidden>
Date: Sun Sep 9 16:17:46 2012 +0200

    sierra: use +CFUN=4 for powering down

commit bee7f0b83fff0c86ae994c75892eef6a4a9584ab
Author: Marius B. Kotsbak <email address hidden>
Date: Tue Oct 30 18:31:52 2012 +0100

    sierra: avoid reset when setting cfun=1

    Some Sierra modems trigger a reset of the modem when sending +cfun=1,
    which is more likely when +cfun=4 is used for powering down since +cfun=1 is
    skipped if mode is already 1. All sierra modems supports a second parameter
    to indicate that no reset is to be done: "+cfun=1,0".

commit 814febe1fd9baacdb33c79f11c140187df36c4f1
Author: Dan Williams <email address hidden>
Date: Tue Oct 30 16:16:25 2012 -0500

    sierra: fix CFUN power up delay handling

    1) all Sierra devices appear to require short delay after powering up,
    otherwise subsequent commands may return errors. Older devices need
    longer so ensure new devices are penalized just for being new.

    2) When the modem is already in full functionality status and no power
    up command was sent, there's no need to delay, which was happening
    regardless of what state the modem was already in. Detect whether
    the power up was actually executed (response and error will be NULL)
    and only delay if it was executed.

and maybe:

commit 10745cb32c5fe3b77bfc95a2a1f51b0896435238
Author: Dan Williams <email address hidden>
Date: Tue Oct 30 18:38:50 2012 -0500

    sierra: allow more time for PDP context activation

    3 seconds isn't always enough to set up the context with the network.