quick heads up. The problem I encountered are related to KVM and the fact that KVM guests use different devices than z/VM guests. but that is broken since 'forever' in the old code (the new NM approach is not affected). Apparently nobody ever tested dumping via the network for a KVM guest on s390...
Ok, I managed to install RHEL-8.8.0-20230113.0 (kernel: 4.18.0-448.el8.s390x) on a z/VM 6.4.0 system. The ifcfg contains the SUBCHANNELS, OPTIONS and NETTYPE fields. So my best guess for now is that it's a z/VM 6.4.0 vs. z/VM 7.2.0 problem.
Patches sent to the mailing list. @Raju: btw, great analysis of the problem. This really helped!
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (kexec-tools bug fix and enhancement update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2023:2953