D-GSM 1/n: add mslookup server in osmo-hlr

Implement the mslookup server to service remote mslookup requests.

This patch merely adds the logic to answer incoming mslookup requests, an
actual method to receive requests (mDNS) follows in a subsequent patch.

- API to configure service names and addresses for the local site (per MSC).
- determine whether a subscriber is on a local MSC
  (checking the local proxy will be added in subsequent patch that adds proxy
  capability).
- VTY config follows in a subsequent patch.

For a detailed overview of the D-GSM and mslookup related files, please see the
elaborate comment at the top of mslookup.c (already added in an earlier patch).

Change-Id: Ife4a61d71926d08f310a1aeed9d9f1974f64178b
diff --git a/include/osmocom/hlr/Makefile.am b/include/osmocom/hlr/Makefile.am
index 532fa5d..5c96ec8 100644
--- a/include/osmocom/hlr/Makefile.am
+++ b/include/osmocom/hlr/Makefile.am
@@ -10,5 +10,7 @@
 	hlr_vty_subscr.h \
 	logging.h \
 	lu_fsm.h \
+	mslookup_server.h \
 	rand.h \
+	timestamp.h \
 	$(NULL)