doc: add item for "-M enforce-config-section"

It's never documented, and now we have one more parameter for it (which
obsoletes this one). Document it properly.
Suggested-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <1499396048-21657-1-git-send-email-peterx@redhat.com>
Reviewed-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
  Removed 'Although now' commit message as per Eduardo's review

qemu-options.hx

@@ -85,6 +85,12 @@ Enables or disables NVDIMM support. The default is off.
 @item s390-squash-mcss=on|off
 Enables or disables squashing subchannels into the default css.
 The default is off.
+@item enforce-config-section=on|off
+If @option{enforce-config-section} is set to @var{on}, force migration
+code to send configuration section even if the machine-type sets the
+@option{migration.send-configuration} property to @var{off}.
+NOTE: this parameter is deprecated. Please use @option{-global}
+@option{migration.send-configuration}=@var{on|off} instead.
 @end table
 ETEXI