qapi-schema: Fix up misleading specification of netdev_add

It doesn't take a 'props' argument, let alone one in the format
"NAME=VALUE,..."

The bogus arguments specification doesn't matter due to 'gen': false.
Clean it up to be incomplete rather than wrong, and document the
incompleteness.

While there, improve netdev_add usage example in the manual: add a
device option to show how it's done.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1442401589-24189-24-git-send-email-armbru@redhat.com>

docs/qapi-code-gen.txt

@@ -471,7 +471,7 @@ try to avoid adding new commands that rely on this, and instead use
 type-safe unions.  For an example of bypass usage:
 
  { 'command': 'netdev_add',
-   'data': {'type': 'str', 'id': 'str', '*props': '**'},
+   'data': {'type': 'str', 'id': 'str'},
    'gen': false }
 
 Normally, the QAPI schema is used to describe synchronous exchanges,

qapi-schema.json

@@ -2079,11 +2079,12 @@
 #
 # @id: the name of the new network backend
 #
-# @props: #optional a list of properties to be passed to the backend in
-#         the format 'name=value', like 'ifname=tap0,script=no'
+# Additional arguments depend on the type.
 #
-# Notes: The semantics of @props is not well defined.  Future commands will be
-#        introduced that provide stronger typing for backend creation.
+# TODO This command effectively bypasses QAPI completely due to its
+# "additional arguments" business.  It shouldn't have been added to
+# the schema in this form.  It should be qapified properly, or
+# replaced by a properly qapified command.
 #
 # Since: 0.14.0
 #
@@ -2091,8 +2092,8 @@
 #          If @type is not a valid network backend, DeviceNotFound
 ##
 { 'command': 'netdev_add',
-  'data': {'type': 'str', 'id': 'str', '*props': '**'},
-  'gen': false }
+  'data': {'type': 'str', 'id': 'str'},
+  'gen': false }                # so we can get the additional arguments
 
 ##
 # @netdev_del:

qmp-commands.hx

@@ -917,7 +917,9 @@ Arguments:
 
 Example:
 
--> { "execute": "netdev_add", "arguments": { "type": "user", "id": "netdev1" } }
+-> { "execute": "netdev_add",
+     "arguments": { "type": "user", "id": "netdev1",
+                    "dnssearch": "example.org" } }
 <- { "return": {} }
 
 Note: The supported device options are the same ones supported by the '-netdev'