debug: use LOGL_NOTICE instead of LOGL_DEBUG

In debug.c the log category DICMP6 uses LOGL_DEBUG as default. This is
way to verbose, lets use LOGL_NOTICE instead.

Change-Id: I4c6a9165114d1240e7e2cfa98d30d571a3f4e9d2
Related: OS#2577

lib/debug.c

@@ -29,7 +29,7 @@ static const struct log_info_cat default_categories[] = {
 	[DICMP6] = {
 		.name = "DICMP6",
 		.description = "ICMPv6",
-		.enabled = 1, .loglevel = LOGL_DEBUG,
+		.enabled = 1, .loglevel = LOGL_NOTICE,
 	},
 };