demo: add testing of UDP

Verification of UDP is added to the demo by forcing machine 2 to
connect to the registry via UDP, we also enable a listening UDP
interface on the registry.

demo/m2/re6stnet.conf

 log m2/
 run m2/run
 state m2/
-pp 1194 tcp
 ca ca.crt
 cert m2/cert.crt
 key m2/cert.key
 default
+disable-proto none
+client 10.0.0.2,1194,udp

demo/registry/re6stnet.conf

@@ -6,3 +6,4 @@ ca ca.crt
 cert registry/cert.crt
 key registry/cert.key
 gateway
+disable-proto none