[BUG] client timeout incorrectly rearmed while waiting for server

[BUG] client timeout incorrectly rearmed while waiting for server

Client timeout could be refreshed in stream_sock_*, but this is
undesired when the timeout is already set to eternity. The effect
is that a session could still be aborted if client timeout was
smaller than server timeout. A second effect is that sessions
expired on the server side would expire with "cD" flags.

The fix consists in not updating it if it was not previously set.
A cleaner method might consist in updating the buffer timeout. This
is probably what will be done later when the state machines only
deal with the buffers.