build: install dbus-org.bluez.obex.service symlink

obex.service has an alias(dbus-org.bluez.obex.service) which is created
as it's enabled. At the same time, the dbus service references the alias
itself.

Thus the dbus socket activation can happen, only when the service is
already enabled/running... Which defeats the whole purpose.

Create/install the respective symlink/alias, so that any user looking
for the dbus will start it.

Note: we need a hook here instead of LN_S to create the in-tree file,
since `install' aggressively dereferences it.

Makefile.obexd

@@ -3,6 +3,12 @@ if SYSTEMD
 systemduserunitdir = $(SYSTEMD_USERUNITDIR)
 systemduserunit_DATA = obexd/src/obex.service
 
+install-data-hook:
+	$(LN_S) -f obex.service $(DESTDIR)$(SYSTEMD_USERUNITDIR)/dbus-org.bluez.obex.service
+
+uninstall-hook:
+	rm -f $(DESTDIR)$(SYSTEMD_USERUNITDIR)/dbus-org.bluez.obex.service
+
 dbussessionbusdir = $(DBUS_SESSIONBUSDIR)
 dbussessionbus_DATA = obexd/src/org.bluez.obex.service
 endif