INT-3578 Fix IllegalArgumentException

JIRA: https://jira.spring.io/browse/INT-3578

Adding `readDelay` to XML namespace for the `TcpConnectionFactoryFactoryBean`
caused an `IllegalArgumentException` when configuring with Java instea of
XML.
Yeah... My fault with https://jira.spring.io/browse/INT-3449.
Another point: if we'd add TCP support to DSL, we'd had catched this issue...