Various logging fixes

Log transaction allocation errors as such. While at it, use proper
subsystem to log missing VLR subscriber.

Change-Id: I617be8793b9416ccd49022c72f7d93df7f4fb4d9
diff --git a/src/libmsc/transaction.c b/src/libmsc/transaction.c
index df770ed..17f8e96 100644
--- a/src/libmsc/transaction.c
+++ b/src/libmsc/transaction.c
@@ -109,7 +109,7 @@
 
 	/* a valid subscriber is indispensable */
 	if (vsub == NULL) {
-		LOGP(DCC, LOGL_NOTICE,
+		LOGP(DVLR, LOGL_ERROR,
 		     "unable to alloc transaction, invalid subscriber (NULL)\n");
 		return NULL;
 	}