docs: update default value of metadata workers for ml2/ovn

[1] changed that value to 0

[1] https://review.opendev.org/c/openstack/neutron/+/861751

Related-Bug: #1993181
Change-Id: I7009e8a9fa8a61cc796d9592db0cf68e07e5884d
(cherry picked from commit 407585f)

Author: bbezak

neutron/conf/agent/metadata/config.py

@@ -94,7 +94,7 @@
     cfg.IntOpt('metadata_workers',
                sample_default='<num_of_cpus> / 2',
                help=_('Number of separate worker processes for metadata '
-                      'server (defaults to 2 when used with ML2/OVN and half '
+                      'server (defaults to 0 when used with ML2/OVN and half '
                       'of the number of CPUs with other backend drivers)')),
     cfg.IntOpt('metadata_backlog',
                default=4096,