Documentation: networking: dsa: add missing new line in devlink section

"make htmldocs" produces these warnings:
Documentation/networking/dsa/dsa.rst:468: WARNING: Unexpected indentation.
Documentation/networking/dsa/dsa.rst:477: WARNING: Block quote ends without a blank line; unexpected unindent.

Fixes: 8411abbc ("Documentation: networking: dsa: mention integration with devlink")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/dsa/dsa.rst

@@ -464,6 +464,7 @@ For each devlink device, every physical port (i.e. user ports, CPU ports, DSA
 links or unused ports) is exposed as a devlink port.
 
 DSA drivers can make use of the following devlink features:
+
 - Regions: debugging feature which allows user space to dump driver-defined
   areas of hardware information in a low-level, binary format. Both global
   regions as well as per-port regions are supported. It is possible to export