docs: netlink: index.rst: add a netlink index file

Instead of generating the index file, use glob to automatically
include all data from yaml.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Reviewed-by: Donald Hunter <[e-mail]>

Documentation/netlink/specs/index.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _specs:
+
+=============================
+Netlink Family Specifications
+=============================
+
+.. toctree::
+   :maxdepth: 1
+   :glob:
+
+   *