mac80211: fix tx fragmentation

This patch fixes TX fragmentation caused by
tx handlers reordering and 'tx info to cb' patches

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