mac80211: re-enable re-transmission of filtered frames

mac80211: re-enable re-transmission of filtered frames

In an earlier commit,

    mac80211: disable software retry for now

    Pavel Roskin reported a problem that seems to be due to
    software retry of already transmitted frames. It turns
    out that we've never done that correctly, but due to
    some recent changes it now crashes in the TX code. I've
    added a comment in the patch that explains the problem
    better and also points to possible solutions -- which
    I can't implement right now.

I disabled software retry of failed/filtered frames
because it was broken. With the work of the previous
patches, it now becomes fairly easy to re-enable it
by adding a flag indicating that the frame shouldn't
be modified, but still running it through the transmit
handlers to populate the control information.

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