wifi(implementation): Copy the user complete callback by value

The callback object may go out of scope by the time it's invoked. So,
make a copy of it. We're doing the same for the other user callbacks
received in this class.

Bug: 34930275
Test: Compiles
Change-Id: I275bba11ae8735a21514d871e8aa473f92f0fd7d
diff --git a/wifi/1.0/default/wifi_legacy_hal.cpp b/wifi/1.0/default/wifi_legacy_hal.cpp
index 40f55a3..cd89acc 100644
--- a/wifi/1.0/default/wifi_legacy_hal.cpp
+++ b/wifi/1.0/default/wifi_legacy_hal.cpp
@@ -350,7 +350,8 @@
     return WIFI_SUCCESS;
   }
   LOG(DEBUG) << "Stopping legacy HAL";
-  on_stop_complete_internal_callback = [&](wifi_handle handle) {
+  on_stop_complete_internal_callback = [on_stop_complete_user_callback,
+                                        this](wifi_handle handle) {
     CHECK_EQ(global_handle_, handle) << "Handle mismatch";
     // Invalidate all the internal pointers now that the HAL is
     // stopped.