qapi: fix example of netdev_add command

Example output has the optional member @dnssearch as string type. It
should be an array of String objects instead. Fix it.

For reference, see NetdevUserOptions.

Signed-off-by: Victor Toso <victortoso@redhat.com>
Message-Id: <20220401110712.26911-1-victortoso@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message tweaked for precision]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qapi/net.json

@@ -51,7 +51,7 @@
 #
 # -> { "execute": "netdev_add",
 #      "arguments": { "type": "user", "id": "netdev1",
-#                     "dnssearch": "example.org" } }
+#                     "dnssearch": [ { "str": "example.org" } ] } }
 # <- { "return": {} }
 #
 ##