CHERRY-PICK: iface-modem: don't rely on the cached current power state value

The real power state value of the modem may be changed by other means, e.g.
rfkill. So when changing power state of the modem in MM, we better recheck
which the current power status is.

A better full approach would be to follow rfkill changes, but this fix should
help until that is done.

https://bugzilla.gnome.org/show_bug.cgi?id=702838
(cherry picked from commit e227d4af39d2c09ef1e8a8818d2558fba210f334)

Change-Id: I0d894fe8b1cab093640a94f0a15153add1925880
Reviewed-on: https://gerrit.chromium.org/gerrit/62064
Commit-Queue: Ben Chan <benchan@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
1 file changed