drbd: Turn conn_flush_workqueue() into drbd_flush_workqueue()

The new function can flush any work queue, not just the work queue of the data
socket of a connection.

Signed-off-by: Andreas Gruenbacher <agruen@linbit.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
4 files changed