Stock configuration for ActiveMQ should specify a JGroups channel instead of a stack

The stock configuration specifies jgroups-stack="udp" in the messaging-activemq subsystem. This appears to cause a second instance of that stack to be created if other subsystems (e.g. Infinispan) are also using it. That second instance appears to cause WFLY-4971.

WildFly still seems happy if I change the jgroups-stack to "ee" (to use the ee channel) or to a fork off the ee channel. The stock configuration should do the same thing to fix WFLY-4971.