dispatcher(k): corrected the variable which is set by ds_is_from_list()

- setid_pvar is used instead of grp_avp
- reported by Dan B.

modules_k/dispatcher/README

@@ -811,7 +811,8 @@ failure_route[tryagain] {
 
    Parameter groupid is optional, when it is missing, then the matching
    will be done against all addresses in all groups. Upon a match, the
-   'grp_avp' will be set to groupid of matching address.
+   variable specified by 'setid_pvar' parameter will be set to groupid of
+   matching address.
 
    This function can be used from ANY_ROUTE.
 

modules_k/dispatcher/doc/dispatcher_admin.xml

@@ -965,7 +965,8 @@ failure_route[tryagain] {
 		<para>
 		Parameter groupid is optional, when it is missing, then the matching
 		will be done against all addresses in all groups. Upon a match, the
-		'grp_avp' will be set to groupid of matching address.
+		variable specified by 'setid_pvar' parameter will be set to groupid
+		of matching address.
  		</para>
 		<para>
 			This function can be used from ANY_ROUTE.