nimble/host: Fix stopping `ble_hs_flow_timer` in `ble_hs_flow_startup`
In `ble_hs_flow_startup`, stopping `ble_hs_flow_timer` before creating it
results in accessing invalid/null `TimerHandle`
@@ -231,7 +231,10 @@ ble_hs_flow_startup(void)
/* Assume failure. */
ble_hci_trans_set_acl_free_cb(NULL, NULL);
+
+#if MYNEWT_VAL(SELFTEST)
ble_npl_callout_stop(&ble_hs_flow_timer);
+#endif
enable_cmd.enable = BLE_HCI_CTLR_TO_HOST_FC_ACL;
