move headers to include/osmocom/hlr

Apply the same headers structure that we keep in most Osmocom source trees:
Keep noinst_HEADERS in include/osmocom/hlr and include them using
  #include <osmocom/hlr/*.h>

The only header kept in src/ is db_bootstrap.h, because it is generated during
build time. If it was built in include/osmocom/hlr, we would need db.o to
depend on db_bootstrap.h in a different subdir, which automake can't do well.

Change-Id: Ic912fe27f545b85443c5fb713d8c3c8aac23c9ad
diff --git a/src/hlr_vty_subscr.c b/src/hlr_vty_subscr.c
index 73dfab6..d2c4c81 100644
--- a/src/hlr_vty_subscr.c
+++ b/src/hlr_vty_subscr.c
@@ -28,8 +28,8 @@
 #include <osmocom/vty/command.h>
 #include <osmocom/core/utils.h>
 
-#include "hlr.h"
-#include "db.h"
+#include <osmocom/hlr/hlr.h>
+#include <osmocom/hlr/db.h>
 
 struct vty;