Fix recvclient() to obey max_idle for output, too

Fix recvclient() to obey max_idle for output, too

recvclient() flushes the output queue before receiving input.  The
receive obeys max_idle, the flush doesn't.

Broken in commit 08b94556 (v4.3.20) "Reimplement max_idle without a
separate thread".  Until then, the idle thread aborted a stuck attempt
to flush output.