The incoming nghttpx-0rtt-uniq header fields from inbound client are
stripped by default.  Use --no-strip-incoming-nghttpx-0rtt-uniq in
order not to strip them.

Fix doc

nghttpx: Add affinity-cookie-secure parameter to backend option

Error callback2

nghttp2_error_callback2 is an extended version of the existing
nghttp2_error_callback by adding error code parameter.  This
deprecates nghttp2_error_callback.

Nghttpx add client serial

Add tls_client_issuer_name log variable and expose it to mruby

integration: Fix issues reported by the `go vet` tool.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>