null_blk: change type of completion_nsec to unsigned long

This commit at least doubles the maximum value for
completion_nsec. This helps in special cases where one wants/needs to
emulate an extremely slow I/O (for example to spot bugs).
Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Signed-off-by: Arianna Avanzini <avanzini@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/null_blk.c

@@ -132,8 +132,8 @@ static const struct kernel_param_ops null_irqmode_param_ops = {
 device_param_cb(irqmode, &null_irqmode_param_ops, &irqmode, S_IRUGO);
 MODULE_PARM_DESC(irqmode, "IRQ completion handler. 0-none, 1-softirq, 2-timer");
 
-static int completion_nsec = 10000;
-module_param(completion_nsec, int, S_IRUGO);
+static unsigned long completion_nsec = 10000;
+module_param(completion_nsec, ulong, S_IRUGO);
 MODULE_PARM_DESC(completion_nsec, "Time in ns to complete a request in hardware. Default: 10,000ns");
 
 static int hw_queue_depth = 64;