app_agent_spool: Fix typo in dtmf features usage desctiption

Fix typo, that specify usage wrong option 'dtmf-features' for CHANNEL() function
instead of correct 'dtmf_features'

ASTERISK-27377 #close

Change-Id: I15ecc829c1035b359584673e12cdb5c9291ac930

CHANGES

@@ -3200,7 +3200,7 @@ chan_agent
    has also been removed, for the same reason.
 
  * The endcall and enddtmf configuration options are removed.  Use the
-   dialplan function CHANNEL(dtmf-features) to set DTMF features on the agent
+   dialplan function CHANNEL(dtmf_features) to set DTMF features on the agent
    channel before calling AgentLogin.
 
 chan_bridge

UPGRADE-12.txt

@@ -94,7 +94,7 @@ AgentLogin and chan_agent:
    reason as the updatecdr option.
 
  - The endcall and enddtmf configuration options are removed.  Use the
-   dialplan function CHANNEL(dtmf-features) to set DTMF features on the agent
+   dialplan function CHANNEL(dtmf_features) to set DTMF features on the agent
    channel before calling AgentLogin.
 
 AgentMonitorOutgoing

apps/app_agent_pool.c

@@ -72,7 +72,7 @@
 			when a new call comes in for the agent.  Login failures will continue in
 			the dialplan with <variable>AGENT_STATUS</variable> set.</para>
 			<para>Before logging in, you can setup on the real agent channel the
-			CHANNEL(dtmf-features) an agent will have when talking to a caller
+			CHANNEL(dtmf_features) an agent will have when talking to a caller
 			and you can setup on the channel running this application the
 			CONNECTEDLINE() information the agent will see while waiting for a
 			caller.</para>
@@ -92,7 +92,7 @@
 			<ref type="application">PauseQueueMember</ref>
 			<ref type="application">UnpauseQueueMember</ref>
 			<ref type="function">AGENT</ref>
-			<ref type="function">CHANNEL(dtmf-features)</ref>
+			<ref type="function">CHANNEL(dtmf_features)</ref>
 			<ref type="function">CONNECTEDLINE()</ref>
 			<ref type="filename">agents.conf</ref>
 			<ref type="filename">queues.conf</ref>