Improve 'socket timeout reached' message

Improve 'socket timeout reached' message

Log the timeout that was triggered and downgrade the
log level to LOG_LEVEL_CONNECT to reduce the log noise
with common debug settings.

The timeout isn't necessary the result of an error and
usually merely indicates that Privoxy's socket timeout
is lower than the relevant timeouts used by client and
server.

Sponsored by: Robert Klemme