doc: Document log_set_print_level RPC

Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Change-Id: Ic9cd5f19b4e487569855a61575ca0cf83b971866
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/4250
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

doc/jsonrpc.md

@@ -708,6 +708,42 @@ Example response:
 }
 ~~~
 
+## log_set_print_level {#rpc_log_set_print_level}
+
+Set the current level at which output will additionally be
+sent to the current console.
+
+### Parameters
+
+Name                    | Optional | Type        | Description
+----------------------- | -------- | ----------- | -----------
+level                   | Required | string      | ERROR, WARNING, NOTICE, INFO, DEBUG
+
+### Example
+
+Example request:
+
+~~~
+{
+  "jsonrpc": "2.0",
+  "method": "log_set_print_level",
+  "id": 1,
+  "params": {
+    "level": "ERROR"
+  }
+}
+~~~
+
+Example response:
+
+~~~
+{
+  "jsonrpc": "2.0",
+  "id": 1,
+  "result": true
+}
+~~~
+
 ## log_enable_timestamps {#rpc_log_enable_timestamps}
 
 Enable or disable timestamps.