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/gsup_send.c b/src/gsup_send.c
index 247a7e7..29aeaa5 100644
--- a/src/gsup_send.c
+++ b/src/gsup_send.c
@@ -21,8 +21,8 @@
 
 #include <errno.h>
 
-#include "gsup_server.h"
-#include "gsup_router.h"
+#include <osmocom/hlr/gsup_server.h>
+#include <osmocom/hlr/gsup_router.h>
 
 #include <osmocom/core/logging.h>