add DLMGCP logging category for libosmo-mgcp

In the course of splitting up the openbsc.git repository, we will create
libosmo-mgcp and need a library logging category for that purpose.

Change-Id: I09c587e2d59472cbde852d467d457254746d9e67
diff --git a/src/logging.c b/src/logging.c
index 2fb06ba..2e913e5 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -161,6 +161,11 @@
 		.description = "libosmo-sigtran MTP3 User Adaptation",
 		.enabled = 1, .loglevel = LOGL_NOTICE,
 	},
+	[INT2IDX(DLMGCP)] = {
+		.name = "DLMGCP",
+		.description = "libosmo-mgcp Media Gateway Control Protocol",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
 };
 
 /*! descriptive string for each log level */