Add libvlr implementation

Original libvlr code is by Harald Welte <laforge@gnumonks.org>,
polished and tweaked by Neels Hofmeyr <nhofmeyr@sysmocom.de>.

This is a long series of trial-and-error development collapsed in one patch.
This may be split in smaller commits if reviewers prefer that. If we can keep
it as one, we have saved ourselves the additional separation work.

Related: OS#1592
Change-Id: Ie303c98f8c18e40c87c1b68474b35de332033622
diff --git a/include/openbsc/debug.h b/include/openbsc/debug.h
index 8a4247b..3feb7c3 100644
--- a/include/openbsc/debug.h
+++ b/include/openbsc/debug.h
@@ -38,12 +38,8 @@
 	DSUA,
 	DV42BIS,
 	DPCU,
+	DVLR,
 	Debug_LastEntry,
 };
 
-struct gsm_subscriber;
-
-void log_set_filter_vlr_subscr(struct log_target *target,
-			       struct gsm_subscriber *vlr_subscr);
-
 extern const struct log_info log_info;