Reflect API rename in docs

Ref 5df6f8d4

doc/sphinx/reference/vmod.rst

@@ -741,15 +741,15 @@ not be left half-initialized should a failure occur.
 If your VMOD is running an asynchronous background job you can hold a reference
 to the VCL to prevent it from going cold too soon and get the same guarantees
 as backends with ongoing requests for instance. For that, you must acquire the
-reference by calling ``VRT_ref_vcl`` when you receive a ``VCL_EVENT_WARM`` and
-later calling ``VRT_rel_vcl`` once the background job is over. Receiving a
+reference by calling ``VRT_VCL_Prevent_Discard`` when you receive a ``VCL_EVENT_WARM`` and
+later calling ``VRT_VCL_Allow_Discard`` once the background job is over. Receiving a
 ``VCL_EVENT_COLD`` is your cue to terminate any background job bound to a VCL.
 
 You can find an example of VCL references in vmod-debug::
 
-	priv_vcl->vclref = VRT_ref_vcl(ctx, "vmod-debug");
+	priv_vcl->vclref = VRT_VCL_Prevent_Discard(ctx, "vmod-debug");
 	...
-	VRT_rel_vcl(&ctx, &priv_vcl->vclref);
+	VRT_VCL_Allow_Discard(&ctx, &priv_vcl->vclref);
 
 In this simplified version, you can see that you need at least a VCL-bound data
 structure like a ``PRIV_VCL`` or a VMOD object to keep track of the reference