The REQUIRE_HOST_HTTP11 attribute was deprecated in Undertow, but not in the integration code for EAP 8.0.x, so there's no actual way to disable it. It is false by default, but even when undefined manually there's a warning logged for every request as the option is always present:

WARN [io.undertow] (default I/O-44) UT005108: Configuration option is no longer supported: REQUIRE_HOST_HTTP11.