qapi: fix example of NIC_RX_FILTER_CHANGED event

Example output has an extra ending curly bracket. Fix it.

Problem was noticed when trying to load the example into python's json
library.

Signed-off-by: Victor Toso <victortoso@redhat.com>
Message-Id: <20220901085840.22520-6-victortoso@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qapi/net.json

@@ -757,7 +757,6 @@
 #      "data": { "name": "vnet0",
 #                "path": "/machine/peripheral/vnet0/virtio-backend" },
 #      "timestamp": { "seconds": 1368697518, "microseconds": 326866 } }
-#    }
 #
 ##
 { 'event': 'NIC_RX_FILTER_CHANGED',