MT#62272 moh: document new config option `moh-prevent-double-hold`

Add a documentation to describe a usage
of `moh-prevent-double-hold`.

Change-Id: I2df2900c2934b15837fd8b12fc639ba746b153fa

docs/ng_control_protocol.md

@@ -2214,6 +2214,11 @@ MoH stream will also be dropped in case of full dialog termination.
 The MoH SDP session can also be marked with a specific (custom) session level attribute.
 For that to enable see the `moh-attr-name` configuration option.
 
+In order to protect against double MoH played, e.g. when inadvertently two rtpengine instances
+in the interaction chain both try to trigger MoH, use `moh-prevent-double-hold` configuration option (true/false).
+It works in combination with `moh-attr-name` config option, which must be defined in order to give a clue to rtpengine,
+what is the session level attribute to be used for a double hold detection.
+
 List of parameters to be given when advertising MoH capabilities:
 
 - a sound source : `file`, `blob` or `db-id`.

docs/rtpengine.md

@@ -1150,6 +1150,16 @@ call to inject-DTMF won't be sent to __\-\-dtmf-log-dest=__ or __\-\-listen-tcp-
     Controls the value to be added to the session level of SDP whenever MoH is triggered.
     If not defined, then not in use.
 
+- __\-\-moh-prevent-double-hold__
+
+    Protects against double MoH played,
+    e.g. when inadvertently two rtpengine instances in the interaction chain both try to trigger MoH.
+
+    Works in combination with __moh-attr-name__, which must be defined in order to give a clue to rtpengine,
+    what is the session level attribute to be used for a double hold detection.
+
+    If not defined, then not in use.
+
 - __\-\-kernel-player=__*INT*
 - __\-\-kernel-player-media=__*INT*