The TCP/TCP_NIO2 transports now implement failure detection without requiring a second socket (via FD_SOCK/FD_SOCK2). [1]
This eliminates the need for a redundant port for TCP-based stacks.
N.B. FD_SOCK2 is still needed for datagram socket-based stacks
N.B. Transport-based failure detection is not compatible with connection reaping (not enabled by default).

[1] http://jgroups.org/manual5/index.html#_failure_detection_in_tcp_and_tcp_nio2