drbd: Introduced tconn->cstate_mutex

In compatibility mode with old DRBDs, use that as the state_mutex
as well.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

diff --cc drivers/block/drbd/drbd_int.h
Simple merge

diff --cc drivers/block/drbd/drbd_main.c
Simple merge

diff --cc drivers/block/drbd/drbd_nl.c
Simple merge

diff --cc drivers/block/drbd/drbd_receiver.c
Simple merge

diff --cc drivers/block/drbd/drbd_state.c
Simple merge

diff --cc drivers/block/drbd/drbd_worker.c
Simple merge