core/logging.h: Add logging category for jitter buffer

Forthcoming jitter buffer code in libosmo-netif will make use of it.

Change-Id: I2434f9dfa401f736bc62a2ddce920e587cd8c517
diff --git a/include/osmocom/core/logging.h b/include/osmocom/core/logging.h
index 617d78e..e68f618 100644
--- a/include/osmocom/core/logging.h
+++ b/include/osmocom/core/logging.h
@@ -121,7 +121,8 @@
 #define DLSUA		-15	/*!< Osmocom SUA */
 #define DLM3UA		-16	/*!< Osmocom M3UA */
 #define DLMGCP		-17	/*!< Osmocom MGCP */
-#define OSMO_NUM_DLIB	17	/*!< Number of logging sub-systems in libraries */
+#define DLJIBUF		-18	/*!< Osmocom Jitter Buffer */
+#define OSMO_NUM_DLIB	18	/*!< Number of logging sub-systems in libraries */
 
 /*! Configuration of single log category / sub-system */
 struct log_category {