[cli] get preferred and supported channel mask (#4253)

src/cli/README.md

@@ -113,6 +113,26 @@ Set the IEEE 802.15.4 Channel value.
 Done
 ```
 
+### channel preferred
+
+Get preferred channel mask.
+
+```bash
+> channel preferred
+0x7fff800
+Done
+```
+
+### channel supported
+
+Get supported channel mask.
+
+```bash
+> channel supported
+0x7fff800
+Done
+```
+
 ### child list
 
 List attached Child IDs.

src/cli/cli.cpp

@@ -460,6 +460,14 @@ void Interpreter::ProcessChannel(int argc, char *argv[])
     {
         mServer->OutputFormat("%d\r\n", otLinkGetChannel(mInstance));
     }
+    else if (strcmp(argv[0], "supported") == 0)
+    {
+        mServer->OutputFormat("0x%x\r\n", otPlatRadioGetSupportedChannelMask(mInstance));
+    }
+    else if (strcmp(argv[0], "preferred") == 0)
+    {
+        mServer->OutputFormat("0x%x\r\n", otPlatRadioGetPreferredChannelMask(mInstance));
+    }
 #if OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE
     else if (strcmp(argv[0], "monitor") == 0)
     {