doc: Document log_get_flags

Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Change-Id: I68fbc371ab360ecc1009d559542ca29671c16c92
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/4256
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

@@ -906,6 +906,38 @@ Example response:
 }
 ~~~
 
+## log_get_flags {#rpc_log_get_flags}
+
+Get the list of valid flags for this application and whether
+they are currently enabled.
+
+### Example
+
+Example request:
+
+~~~
+{
+  "jsonrpc": "2.0",
+  "method": "log_get_flags",
+  "id": 1,
+}
+~~~
+
+Example response:
+
+~~~
+{
+  "jsonrpc": "2.0",
+  "id": 1,
+  "result": {
+    "nvmf": true,
+    "nvme": true,
+    "aio": false,
+    "bdev" false
+  }
+}
+~~~
+
 ## log_enable_timestamps {#rpc_log_enable_timestamps}
 
 Enable or disable timestamps.