[S390] qdio: clear shared DSCI before scheduling the queue handler

[S390] qdio: clear shared DSCI before scheduling the queue handler

The following race can occur with qdio devices that use the shared device
state change indicator:

Device (Shared DSCI)    CPU0                            CPU1
===============================================================================

1. DSCI 0 => 1,
   INT pending
                        2. Thinint handler
                        * si_used = 1
                        * Inbound tasklet_schedule
                        * DSCI 1 => 0

3. DSCI 0 => 1,
   INT pending

                                                        4. Thinint handler
                                                        * si_used = 1
                                                        * Inbound tasklet_schedu
le
                                                           => NOP

                        5. Inbound tasklet run

6. DSCI = 1,
   INT surpressed

                                                        7. DSCI 1 => 0

The race would lead to a stall where new data in the input queue is
not recognized so the device stops working in case of no further traffic.

Fix the race by resetting the DSCI before scheduling the inbound tasklet
so the device generates an interrupt if new data arrives in the above
scenario in step 6.

Reviewed-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>