s390/sclp: Change SCLP console default buffer-full behavior

Dropping kernel messages during a console-buffer-full condition
is preferable to halting the system until console messages are
delivered, especially for production systems.

Update default for sclp_console_drop kernel parameter accordingly.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@linux.vnet.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>