Convert the assoc_active boolean flag to a bitop on the flags field.
The bit ops will provide atomicity.
To make this change, the flags field was converted to a long type,
which also affects the FCCTRL_TERMIO flag. Both FCCTRL_TERMIO and
now ASSOC_ACTIVE flags are set/cleared by bit operations.
Signed-off-by: James Smart <jsmart2021@gmail.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>