Adding '=’ between ‘g’ and ‘=’ (ifcfg=="192…) worked. I noticed a message during init indicating networking had been configured, and network setup in installer GUI agreed (nothing to do).
Yep, so using a wild card (as outlined in the wiki) for all interfaces works as expected.
All sorted now?
Mostly. There’s still 1182592 – 15.3 installation obliterated custom EFI bootloader entry "opensusetw" yet to catch developer attention, 15.3 taking 4X as long as TW to boot to figure out, a need for online repos to match DVD content, and a need for more sleep to make brain work better. 
I may try to reproduce this in a VM.
I’m not seeing that problem. But my altlernative name is “tumbleweed” and not “opensusetw” that you are using. Perhaps it is removing every entry that contains the string “opensuse”. I seem to recall a bug report on that several years ago, but it was fixed. Maybe the fix never made it to SLE, and with Jump that brings back the bug.
15.3 taking 4X as long as TW to boot to figure out,
I am not seeing that. But I’ll recheck if I setup a system to reproduce the other problem.
As far as I know, they are aware of this problem and working on it.