Upgrade library `esockd` from 5.9.6 to 5.9.7

This upgrade included
* Enhancements regarding proxy protocol error and timeout. [esockd pr#178](https://github.com/emqx/esockd/pull/178)
* Lowered `ssl_error` exceptions to info level logging. [esockd pr#180](https://github.com/emqx/esockd/pull/180)
* Malformed MQTT packet parsing exception log level is lowered from `error` to `info`.
* In command `emqx ctl listeners` output, the `shutdown_count` counter is incremented
  when TLS handshake failure (`ssl_error`) or Malformed packet (`frame_error`) happens.