BUG/MEDIUM: checks: tcp-check: do not poll when there's nothing to send

A config with just a "tcp-check expect string XXX" loops at 100% CPU
because the connect() wakes the function and there's nothing to send,
but it does not disable the polling.

Rearrange the polling setup to fix this. This was just caused by latest
commit, no backport is needed.
1 file changed