mac80211: cleanup reorder buffer handling

The reorder buffer handling is written in a quite
peculiar style (especially comments) and also has
a quirk where it invokes the entire reorder code
in ieee80211_sta_manage_reorder_buf() for just a
handful of lines in it with a special argument.

Split out ieee80211_release_reorder_frames which
can then be invoked from BAR handling and other
reordering code, clean up code and comments and
remove function arguments that are now unused from
ieee80211_sta_manage_reorder_buf().

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