While debugging JENKINS-23917 I noticed that the slave option:
-tcp FILE : instead of talking to the master via
stdin/stdout, listens to a random local
port, write that port number to the given
file, then wait for the master to connect to
that port.
doesn't seem to have any UI in Jenkins node configuration to actually use it, at least for ssh or jnlp slaves. You can specify it as a command line suffix, but there's no way to tell Jenkins that it should make a connection to the agent.
Minor, as it's not super useful for an ssh slave, and for a jnlp slave it's already using JNLP by connecting to the Jenkins master. I only noticed it while debugging.
Perhaps it's best to just remove it from the help output or note that it's for future use?