TLS peer-verification bypass via mid-transfer ssl_config mutation

We want to report a TLS peer-verification issue on current master. The trigger is narrow and requires a specific application usage pattern, but when it fires, a transfer that requests `CURLOPT_SSL_VERIFYPEER=1` can reuse a TLS connection that was established with peer verification disabled. Both …

void Curl_ssl_conn_config_update(struct Curl_easy *data, bool for_proxy)
{
  if(data->conn) {
    struct ssl_primary_config *src, *dest;
    src  = &data->set.ssl.primary;
    dest = &data->conn->ssl_config;
    dest->verifyhost  = src->verifyhost;
    dest->verifypeer  = src->verifypeer; …