SSL: disabled renegotiation detection in client mode. CVE-2009-3555 is no longer relevant and mitigated by the renegotiation info extension (secure renegotiation). On the other hand, unexpected renegotiation still introduces potential security risks, and hence we do not allow renegotiation on the server side, as we never request renegotiation. On the client side the situation is different though. There are backends which explicitly request renegotiation, and disabled renegotiation introduces interoperability problems. This change allows renegotiation on the client side, and fixes interoperability problems as observed with such backends (ticket #872). Additionally, with TLSv1.3 the SSL_CB_HANDSHAKE_START flag is currently set by OpenSSL when receiving a NewSessionTicket message, and was detected by nginx as a renegotiation attempt. This looks like a bug in OpenSSL, though this change also allows better interoperability till the problem is fixed.