iwlwifi: automatically adjust sleep level

Depending on required latency requested by pm_qos (via mac80211)
we can automatically adjust the sleep state. Also, mac80211 has
a user-visible dynamic sleep feature where we are supposed to
stay awake after sending/receiving frames to better receive
response frames to our packets, this can be integrated into the
sleep command.

Currently, and this patch doesn't change that yet, we default
to using sleep level 1 if PS is enabled. With a module parameter
to iwlcore, automatic adjustment to changing network latency
requirements can be enabled -- this isn't yet the default due
to requiring more testing.

The goal is to enable automatic adjustment and then go into the
deepest possible sleep state possible depending on the networking
latency requirements.

This patch does, however, enable IEEE80211_HW_SUPPORTS_DYNAMIC_PS
to avoid the double-timer (one in software and one in the device)
when transmitting -- the exact timeout may be ignored but that is
not of big concern.

Note also that we keep the hard-coded power indices around for
thermal throttling -- the specification of that calls for using
the specified power levels. Those can also be selected in debugfs
to allow easier testing of such parameters.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>