libctrl: Add DLCTRL as logging context for the control interface

... and make libctrl code use it
diff --git a/include/osmocom/core/logging.h b/include/osmocom/core/logging.h
index caeea06..3c5e7b1 100644
--- a/include/osmocom/core/logging.h
+++ b/include/osmocom/core/logging.h
@@ -67,7 +67,8 @@
 #define DLMI		-5
 #define DLMIB		-6
 #define DLSMS		-7
-#define OSMO_NUM_DLIB	7
+#define DLCTRL		-8
+#define OSMO_NUM_DLIB	8
 
 struct log_category {
 	uint8_t loglevel;