Add 6dof to the list of supported gvr features

While reimplementing gvr_experimental_is_feature_supported() as
gvr_is_feature_supported() I accidentally removed 6dof from the list of
supported features.

Bug: 34742071
Test: -
Change-Id: Ic0c9754d72a704d6bfd74dd7a14bdf6e89ed4dd4
diff --git a/libs/vr/libgvr/shim_gvr.cpp b/libs/vr/libgvr/shim_gvr.cpp
index fa8a655..5eb6e3d 100644
--- a/libs/vr/libgvr/shim_gvr.cpp
+++ b/libs/vr/libgvr/shim_gvr.cpp
@@ -512,7 +512,8 @@
 }
 
 bool gvr_is_feature_supported(const gvr_context* /*gvr*/, int32_t feature) {
-  return feature == GVR_FEATURE_ASYNC_REPROJECTION;
+  return feature == GVR_FEATURE_ASYNC_REPROJECTION ||
+      feature == GVR_FEATURE_HEAD_POSE_6DOF;
 }
 
 /////////////////////////////////////////////////////////////////////////////