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/include/Makefile.am b/include/Makefile.am
index dac7011..d8eb1ec 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -1,2 +1,3 @@
-nobase_include_HEADERS = osmocom/gsupclient/gsup_client.h
+SUBDIRS = osmocom
 
+nobase_include_HEADERS = osmocom/gsupclient/gsup_client.h