cfg: fix error in RTPENGINE part, also load module

etc/kamailio.cfg

@@ -282,8 +282,12 @@ loadmodule "presence_xml.so"
 
 #!ifdef WITH_NAT
 loadmodule "nathelper.so"
+#!ifdef WITH_RTPENGINE
+loadmodule "rtpengine.so"
+#!else
 loadmodule "rtpproxy.so"
 #!endif
+#!endif
 
 #!ifdef WITH_TLS
 loadmodule "tls.so"