fix crash on shutdown

we were calling llarp::Context::HandleSignal from a non mainloop
thread when running as a win32 service. this caused issues with a non
clean destruction.

call our signal handler instead of llarp::Context::HandleSignal

daemon/lokinet.cpp

@@ -601,6 +601,7 @@ SvcCtrlHandler(DWORD dwCtrl)
       // tell service we are stopping
       llarp::log::debug(logcat, "Windows service controller gave SERVICE_CONTROL_STOP");
       llarp::sys::service_manager->system_changed_our_state(llarp::sys::ServiceState::Stopping);
+      handle_signal(SIGINT);
       return;
 
     case SERVICE_CONTROL_INTERROGATE:

llarp/win32/service_manager.cpp

@@ -48,7 +48,6 @@ namespace llarp::sys
     if (st == ServiceState::Stopping)
     {
       we_changed_our_state(st);
-      m_Context->HandleSignal(SIGINT);
     }
   }