  "flag_state" : true|false,    (boolean) The new state of the flag
  "warnings" : "str"            (string, optional) Any warnings associated with the change
}

Examples:
> bitcoin-cli setwalletflag avoid_reuse
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "setwalletflag", "params": ["avoid_reuse"]}' -H 'content-type: text/plain;' http://127.0.0.1:8332/


