Use AIDL callbacks directly.

Bug: 210498497
Test: build cuttlefish with ag/16322062, watch logs
Change-Id: I1e0cd95f5f9a911564d14be2d8bbb328572de8c8
diff --git a/radio/aidl/compat/libradiocompat/messaging/RadioMessaging.cpp b/radio/aidl/compat/libradiocompat/messaging/RadioMessaging.cpp
index c1a82b5..79e7c01 100644
--- a/radio/aidl/compat/libradiocompat/messaging/RadioMessaging.cpp
+++ b/radio/aidl/compat/libradiocompat/messaging/RadioMessaging.cpp
@@ -29,6 +29,10 @@
 namespace aidl = ::aidl::android::hardware::radio::messaging;
 constexpr auto ok = &ScopedAStatus::ok;
 
+std::shared_ptr<aidl::IRadioMessagingResponse> RadioMessaging::respond() {
+    return mRadioResponse->messagingCb();
+}
+
 ScopedAStatus RadioMessaging::acknowledgeIncomingGsmSmsWithPdu(  //
         int32_t serial, bool success, const std::string& ackPdu) {
     LOG_CALL << serial << ' ' << success << ' ' << ackPdu;