libbinder_ndk: fix vendor<->vendor transactions.

Before, BpBinder was blocking these since kLocalStability was always
vendor.

Fixes: 142658240
Test: binderVendorDoubleLoadTest
Change-Id: I898a76fc35ed6a15e783b53e925ec47877790b7c
diff --git a/libs/binder/ndk/ibinder.cpp b/libs/binder/ndk/ibinder.cpp
index b06ca86..e752c45 100644
--- a/libs/binder/ndk/ibinder.cpp
+++ b/libs/binder/ndk/ibinder.cpp
@@ -17,6 +17,7 @@
 #include <android/binder_ibinder.h>
 #include "ibinder_internal.h"
 
+#include <android/binder_stability.h>
 #include <android/binder_status.h>
 #include "parcel_internal.h"
 #include "status_internal.h"
@@ -542,7 +543,8 @@
         return STATUS_UNKNOWN_TRANSACTION;
     }
 
-    if ((flags & ~FLAG_ONEWAY) != 0) {
+    constexpr binder_flags_t kAllFlags = FLAG_PRIVATE_VENDOR | FLAG_ONEWAY;
+    if ((flags & ~kAllFlags) != 0) {
         LOG(ERROR) << __func__ << ": Unrecognized flags sent: " << flags;
         return STATUS_BAD_VALUE;
     }