in_syslog: add receive_buffer_size parameter

Signed-off-by: Shizuo Fujita <[email protected]>

input/syslog.md

@@ -105,6 +105,25 @@ The protocol of the `syslog` transport.
 
 See **How to Enable TLS Encryption** section for how to use and see [Configuration Example](../plugin-helper-overview/api-plugin-helper-server.md#configuration-example) for all supported parameters.
 
+#### `receive_buffer_size`
+
+| type | default | version |
+| :--- | :--- | :--- |
+| size | nil | 1.8.0 |
+
+The max size of socket receive buffer for UDP. This is used in `SO_RCVBUF` socket option.
+
+```text
+<source>
+  @type syslog
+  tag system
+  <transport udp>
+    receive_buffer_size 4194304 # 4 MB
+  </transport>
+  # other parameters
+</source>
+```
+
 ### `message_length_limit`
 
 | type | default | version |