softlockup: increase hung tasks check from 2 minutes to 8 minutes

Andrew says:

> Seems that about 100% of the reports we get of this warning triggering
> are sys_sync, transaction commit, etc.

increase the timeout. If it still triggers for people, we can kill it.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/softlockup.c

@@ -164,7 +164,7 @@ unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
 /*
  * Zero means infinite timeout - no checking done:
  */
-unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
+unsigned long __read_mostly sysctl_hung_task_timeout_secs = 480;
 
 unsigned long __read_mostly sysctl_hung_task_warnings = 10;