Increase http_resp_hdr_len and http_req_hdr_len
Increase http_resp_hdr_len and http_req_hdr_len

We're seeing at least up to 4k in the wild, so increase the limit
somewhat.

See: #939

ssm/pkg-varnish,ssm/pkg-varnish,wikimedia/operations-debs-varnish,wikimedia/operations-debs-varnish,ssm/pkg-varnish,wikimedia/operations-debs-varnish,ssm/pkg-varnish,wikimedia/operations-debs-varnish,ssm/pkg-varnish,wikimedia/operations-debs-varnish