nimble/host: Add dummy implementation for ISO rx

This just frees the buffer since host does not handle them (yet).

nimble/host/src/ble_hs.c

@@ -799,6 +799,14 @@ ble_transport_to_hs_acl_impl(struct os_mbuf *om)
     return ble_hs_rx_data(om, NULL);
 }
 
+int
+ble_transport_to_hs_iso_impl(struct os_mbuf *om)
+{
+    os_mbuf_free_chain(om);
+
+    return 0;
+}
+
 void
 ble_transport_hs_init(void)
 {