Change to the new Ryu event library

Ryu v2.0 changed from using gevent for event handling towards its own
ryu.lib.hub implementation, and introduces a dependency on the eventlet
library. This patch fixes rfproxy to work against newer such versions of
Ryu.

This is not backward-compatible with earlier versions of Ryu.

Signed-off-by: Joe Stringer <joestringernz@gmail.com>
Reduce scope of IPC

Signed-off-by: Joe Stringer <joestringernz@gmail.com>