Add getOemNetd method to INetd.aidl

OEM could get their customized OemNetd binder by this method

Bug: 120251561
Test: built, flashed, booted
        system/netd/tests/runtests.sh pass

Change-Id: I40696573c99798cab609816675ec9070d1311b91
diff --git a/server/NetdNativeService.cpp b/server/NetdNativeService.cpp
index c2598ce..ab64973 100644
--- a/server/NetdNativeService.cpp
+++ b/server/NetdNativeService.cpp
@@ -1254,5 +1254,11 @@
     return binder::Status::ok();
 }
 
+binder::Status NetdNativeService::getOemNetd(android::sp<android::IBinder>* listener) {
+    ENFORCE_NETWORK_STACK_PERMISSIONS();
+    *listener = nullptr;
+    return binder::Status::ok();
+}
+
 }  // namespace net
 }  // namespace android