MT#17709 remove only 1st occurrence of the key from the call-id list

The count argument influences the operation in the following ways:
   * count > 0: Remove elements equal to value moving from head to tail.
   * count < 0: Remove elements equal to value moving from tail to head.
   * count = 0: Remove all elements equal to value.

Change-Id: Ia77b760fcada0027fe58a48f4b335d5c264e8917

ngcp/dlgcnt.lua

@@ -131,7 +131,7 @@ end
         if not self._test_connection(self.pair) then
             self.pair = self._connect(self.config.pair);
         end
-        local num = self.pair:lrem(callid, 0, key);
+        local num = self.pair:lrem(callid, 1, key);
         sr.log("dbg", string.format("pair:lrem[%s]=>[%s] %d\n", callid, key, num));
         if not self._test_connection(self.central) then
             self.central = self._connect(self.config.central);

tests/ngcp_dlgcnt.lua

@@ -230,5 +230,20 @@ TestNGCPDlgCnt = {} --class
         assertTrue(res)
     end
 
+    function TestNGCPDlgCnt:test_del_key()
+        self.pair:ping() ;mc :returns(true)
+        self.pair:lrem("callid0", 1, "key1") ;mc :returns(1)
+
+        self.central:ping() ;mc :returns(true)
+        self.central:decr("key1")  ;mc :returns(1)
+
+        mc:replay()
+        self.dlg:del_key("callid0", "key1")
+        mc:verify()
+
+        assertIs(self.dlg.central, self.central)
+        assertIs(self.dlg.pair, self.pair)
+    end
+
 -- class TestNGCPDlgCnt
 --EOF