printk: Add KERN_DEFAULT printk log-level

This adds a KERN_DEFAULT loglevel marker, for when you cannot decide
which loglevel you want, and just want to keep an existing printk
with the default loglevel.

The difference between having KERN_DEFAULT and having no log-level
marker at all is two-fold:

 - having the log-level marker will now force a new-line if the
   previous printout had not added one (perhaps because it forgot,
   but perhaps because it expected a continuation)

 - having a log-level marker is required if you are printing out a
   message that otherwise itself could perhaps otherwise be mistaken
   for a log-level.

Signed-of-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 066bb1e..1b2e174 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -97,6 +97,8 @@
 #define	KERN_INFO	"<6>"	/* informational			*/
 #define	KERN_DEBUG	"<7>"	/* debug-level messages			*/
 
+/* Use the default kernel loglevel */
+#define KERN_DEFAULT	"<d>"
 /*
  * Annotation for a "continued" line of log printout (only done after a
  * line that had no enclosing \n). Only to be used by core/arch code