LEAP/TW aarch64 on RPi-3B+ require Ethernet connection for booting?

I’ve recently installed Leap 15.1 and TW 5.1.3 on a Raspberry Pi-3B+, and in both cases the boot process hangs with the message:
lan78xx-eth waiting for PHY auto negotiation to complete

If I plug in the EN cable, it resumes booting. But normally I won’t have this RPi where an EN connection is easily available.

I can’t see any documentation about where this option is enabled (or disabled). In prior releases (e.g., TW 4-20.2), having an EN connection wasn’t required for booting, and my Pi would happily boot up and connect to WiFi, with no EN connection.

Suggestions as to how I can return to that happy state?