Respect "SSLConnect" option for incoming connections

Don't accept incoming plain-text ("non SSL") server connections for
servers configured with "SSLConnect" enabled.

If "SSLConnect" is not set for an incoming connection the server still
accepts both plain-text and encrypted connections.

This change prevents an authenticated client-server being able to force
the server-server to send its password on a plain-text connection when
SSL/TLS was intended.