SilcAsyncOperation
    silc_ske_rekey_initiator(SilcSKE ske,
                             SilcPacketStream stream,
                             SilcSKERekeyMaterial rekey);

    Starts SILC Key Exchange key regeneration (rekey) protocol.  The `rekey'
    is the rekey material received earlier in SilcSKECompletionCb.  That
    same callback is called after the rekey protocol is over to deliver new
    key material and new rekey material.  When the rekey is completed the
    SKE library will automatically update the new keys into `stream'.  The
    completion callback is called after the new keys has been taken into
    use.

    This function returns SilcAsyncOperation operation context which can
    be used to control the protocol from the application.  Application may
    for example safely abort the protocol at any point, if needed.  Returns
    NULL on error.