docs: uapi: netlink: update netlink specs link

With the recent parser_yaml extension, and the removal of the
auto-generated ReST source files, the location of netlink
specs changed.

Update uAPI accordingly.

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

Documentation/userspace-api/netlink/index.rst

···
 
 See also:
  - :ref:`Documentation/core-api/netlink.rst <kernel_netlink>`
- - :ref:`Documentation/networking/netlink_spec/index.rst <specs>`
+ - :ref:`Documentation/netlink/specs/index.rst <specs>`

Documentation/userspace-api/netlink/specs.rst

···
 Internally kernel uses the YAML specs to generate:
 
  - the C uAPI header
- - documentation of the protocol as a ReST file - see :ref:`Documentation/networking/netlink_spec/index.rst <specs>`
+ - documentation of the protocol as a ReST file - see :ref:`Documentation/netlink/specs/index.rst <specs>`
  - policy tables for input attribute validation
  - operation tables