1.0: in_syslog: Add a new parameter send_keepalive_packet

Since 1.14.0: fluent/fluentd#3474

Signed-off-by: Takuro Ashie <ashie@clear-code.com>

Author: ashie

input/syslog.md

@@ -247,6 +247,14 @@ Emitted record is `{"unmatched_line" : "incoming line"}` with `${tag parameter}.
 
 Tries to resolve hostname from IP addresses or not. Cannot set `false` when `source_hostname_key` is set.
 
+### `send_keepalive_packet`
+
+| type | default | version |
+| :--- | :--- | :--- |
+| bool | false | 1.14.0 |
+
+Enables the TCP keepalive for sockets. See [socket article](../plugin-helper-overview/api-plugin-helper-socket.md#send_keepalive_packet-usecase) for more details.
+
 ### `source_hostname_key`
 
 | type | default | version |