mgmt: add support for enabling/disabling IPv4 or v6 channels

refs: #1461

Change-Id: I00bda4098c9a7722bce9d498acce339809af3f01
diff --git a/nfd.conf.sample.in b/nfd.conf.sample.in
index b825cca..11cd009 100644
--- a/nfd.conf.sample.in
+++ b/nfd.conf.sample.in
@@ -50,12 +50,17 @@
   {
     listen yes ; set to 'no' to disable TCP listener, default 'yes'
     port 6363 ; TCP listener port number
+    enable_v4 yes ; set to 'no' to disable IPv4 channels, default 'yes'
+    enable_v6 yes ; set to 'no' to disable IPv6 channels, default 'yes'
   }
 
   ; The udp section contains settings of UDP faces and channels.
+  ; UDP channel is always listening; delete udp section to disable UDP
   udp
   {
     port 6363 ; UDP unicast port number
+    enable_v4 yes ; set to 'no' to disable IPv4 channels, default 'yes'
+    enable_v6 yes ; set to 'no' to disable IPv6 channels, default 'yes'
     idle_timeout 600 ; idle time (seconds) before closing a UDP unicast face
     keep_alive_interval 25; interval (seconds) between keep-alive refreshes