Returns the current TLS protocol version, which may be
gio.types.TlsProtocolVersion.Unknown if the connection has not handshaked, or
has been closed, or if the TLS backend has implemented a protocol version
that is not a recognized #GTlsProtocolVersion.
Returns the current TLS protocol version, which may be gio.types.TlsProtocolVersion.Unknown if the connection has not handshaked, or has been closed, or if the TLS backend has implemented a protocol version that is not a recognized #GTlsProtocolVersion.