mac80211: fix a few work bugs

mac80211: fix a few work bugs

Kalle and Lennert reported problems with the new work
code, and at least Kalle's problem I was able to trace
to a missing jiffies initialisation.

I also ran into a problem where occasionally I couldn't
connect, which seems fixed with kicking the work items
after scanning.

Finally, also add some sanity checking code to verify
that we're not adding work items while an interface is
down -- that case could lead to something similar to
what Lennert was seeing.

There still seems to be a race condition that we're
trying to figure out separately.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Tested-by: Lennert Buytenhek <buytenh@marvell.com>
Tested-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>