core/service: Fix setting connecting state

If the profile don't implement .accept callback it means it cannot
connect in this mode, which is normally used for GATT profiles, so the
code shall not assume the service will start connecting and instead just
return an error.
diff --git a/src/service.c b/src/service.c
index 0da14ab..f387fc4 100644
--- a/src/service.c
+++ b/src/service.c
@@ -197,7 +197,7 @@
 	}
 
 	if (!service->profile->accept)
-		goto done;
+		return -ENOSYS;
 
 	err = service->profile->accept(service);
 	if (!err)