mac80211: resume properly, add suspend/resume test

When mac80211 resumes, it currently doesn't reconfigure the interfaces
entirely and also doesn't reconfigure BSS information -- fix this.

Also, to be able to test this, add a debugfs file that just calls
the suspend/resume code to see what happens when we go through that,
without needing the time-consuming suspend/resume cycle.

(Original version broke the build for CONFIG_PM=n.  Define alternative
functions for that situation. -- JWL)

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