JIRA: https://jira.spring.io/browse/INT-4366
The `MulticastSendingMessageHandler.getSocket()` doesn't guard around
`this.multicastSocket` property causing `NPE` and other inconsistency
in the multi-threaded environment
* Make the whole `MulticastSendingMessageHandler.getSocket()` as
`synchronized` like it is with the super method
* Reuse `closeSocketIfNeeded()` in the
`UnicastSendingMessageHandler.handleMessageInternal()`
* Fix type in the `UnicastSendingMessageHandler` logging message
* Fix `UdpChannelAdapterTests` for missed `BeanFactory` for the SpEL
and also `MulticastSendingMessageHandler.stop()` in one missed places
**Cherry-pick to 4.3.x**
# Conflicts:
# spring-integration-ip/src/main/java/org/springframework/integration/ip/udp/UnicastSendingMessageHandler.java
6a86f5231d