OR-in AMPDU flags rather than assigning them. This lets the TX status for
aggregated packets be processed by rs_tx_status.
Signed-off-by: Daniel C Halperin <daniel.c.halperin@intel.com> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> Signed-off-by: John W. Linville <linville@tuxdriver.com>