buffers: support disabling allocation per numa domain

Currently, the per-numa buffer allocation doesn't support skipping the
allocation altogether for a particular NUMA domain - if it's set to
zero, it instead uses the default allocation.

Therefore, this changes the behavior so that the default is only used
if no per-numa allocation is specified, and an allocation of zero
is honored by not allocating a buffer at all.

Type: improvement
Change-Id: Ie9133b179a88eb884aa3da921e65292daea0df2d
Signed-off-by: Lukas Stockner <lstockner@genesiscloud.com>
diff --git a/docs/configuration/reference.rst b/docs/configuration/reference.rst
index d288a6d..2a7726c 100644
--- a/docs/configuration/reference.rst
+++ b/docs/configuration/reference.rst
@@ -552,7 +552,9 @@
 ^^^^^^^^^^^^^^^
 
 The number of buffers allocated for this specific NUMA domain.
-Default is 0, which falls back to the value configured in **buffers-per-numa**.
+If this is set to zero, no buffers are allocated for this domain.
+
+By default, the value configured in **buffers-per-numa** is used.
 
 .. code-block:: console