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/tests/gsup_server/gsup_server_test.c b/tests/gsup_server/gsup_server_test.c
index cc475be..4aec69b 100644
--- a/tests/gsup_server/gsup_server_test.c
+++ b/tests/gsup_server/gsup_server_test.c
@@ -20,7 +20,7 @@
 
 #include <stdio.h>
 #include <osmocom/core/utils.h>
-#include "gsup_server.h"
+#include <osmocom/hlr/gsup_server.h>
 
 #define comment_start() printf("\n===== %s\n", __func__)
 #define comment_end() printf("===== %s: SUCCESS\n\n", __func__)