libctrl: Add DLCTRL as logging context for the control interface

... and make libctrl code use it
diff --git a/src/logging.c b/src/logging.c
index 2e3a80a..f9d789d 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -106,6 +106,11 @@
 		.enabled = 1, .loglevel = LOGL_NOTICE,
 		.color = "\033[1;38m",
 	},
+	[INT2IDX(DLCTRL)] = {
+		.name = "DLCTRL",
+		.description = "Control Interface",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
 };
 
 /*! \brief descriptive string for each log level */