mac80211: fix key todo list order

When we add multiple todo entries, we rely on them being executed
mostly in the right order, especially when a key is being replaced.
But when a default key is replaced, the todo list order will differ
from the order when the key being replaced is not a default key, so
problems will happen. Hence, just move each todo item to the end of
the list when it is added so we can in the other code ensure that
hw accel for a key will be disabled before it is enabled for the
replacement.

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