MINOR: unix: don't mention free ports on EAGAIN

When a connect() to a unix socket returns EAGAIN we talk about
"no free ports" in the error/debug message, which only makes
sense when using TCP.

Explain connect() failure and suggest troubleshooting server
backlog size.
(cherry picked from commit 9f256d4d85f2b9c79b0d4f28a27731260eefa1b2)
(cherry picked from commit ffcc8a9e05caec1def8db8f5218e2ecad264a2d4)
1 file changed