configs/features.conf: Add documentation noting potential chan_agent conflict

In chan_agent, a '*' is used by default to terminate a bridge with a caller.
This can lead to all sorts of problems if '*' is used by a feature in
features.conf, as the chan_agent disconnect '*' may be detected first.

This patch adds a documentation snippet to features.conf so that users who
attempt to use features with agents know of the potential conflict.

ASTERISK-20402 #close
Reported by: Matt Riddell
patches:
  features.conf.diff uploaded by Matt Riddell (License 5023)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@427617 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/features.conf.sample

@@ -152,6 +152,8 @@ context => parkedcalls          ; Which context parked calls are in (default is
 [featuremap]
 ;blindxfer => #1                ; Blind transfer  (default is #) -- Make sure to set the T and/or t option in the Dial() or Queue() app call!
 ;disconnect => *0               ; Disconnect  (default is *) -- Make sure to set the H and/or h option in the Dial() or Queue() app call!
+                                ; Note that Agents via chan_agent use * to disconnect a call by default. If you are wanting to use * 
+                                ; to abort a transfer you will either need to change the disconnect code here or set endcall to no in agents.conf 
 ;automon => *1                  ; One Touch Record a.k.a. Touch Monitor -- Make sure to set the W and/or w option in the Dial() or Queue() app call!
 ;atxfer => *2                   ; Attended transfer  -- Make sure to set the T and/or t option in the Dial() or Queue()  app call!
 ;parkcall => #72                ; Park call (one step parking)  -- Make sure to set the K and/or k option in the Dial() app call!