[appserver-io/webserver] Fix DoS danger in secure client-initiated renegotiation of connections

[wick-ed]

The feature of a secure client-initiated renegotiation of TLS/SSL connections makes a server vulnerable to a certain kind of very effective (D)DoS attack.
@see https://community.qualys.com/blogs/securitylabs/2011/10/31/tls-renegotiation-and-denial-of-service-attacks

Several testing tools (including https://www.ssllabs.com) do mention this as a possible danger.

UAC:

• The risk of a DoS attack over the described vector MUST be minimized
• The feature SHOULD not be removed in order to do so
• The feature COULD be removed if absolutely necessary