Reverts and further refines 1d757f4

See #2847
This one was merged with not enough testing : it turns out the kernel
arg is only visible to dracut, which turns it into a drop-in file, in
/etc/cmdline.d/60kdumpip.conf

Adding this as a condition to the sysroot.mount generator makes systemd
skip the mount unit in kdump initramfs (only when kdump is configured to
export logs to a remote IP)

Ref https://issues.redhat.com/browse/OCPBUGS-29762

overlay.d/05core/usr/lib/dracut/modules.d/35coreos-ignition/coreos-diskful-generator

@@ -67,14 +67,14 @@ mkdir -p ${UNIT_DIR}
 # to run if there's already a root= karg, where the systemd-fstab-generator
 # should win.
 # We also don't want to generate sysroot.mount if we are booting a kdump kernel
-# that aims to upload logs to a remote target, as the XFS kernel module won't be loaded
+# that aims to upload logs to a remote target, as we may be in a diskless setup
 # https://issues.redhat.com/browse/OCPBUGS-27935
-# FIXME: this kdump case should be removed when we are done with https://github.com/coreos/fedora-coreos-tracker/issues/1675
-if test -n "$(cmdline_arg ostree)" && test -z "$(cmdline_arg root)" && test -z "$(cmdline_arg kdump_remote_ip)"; then
+if test -n "$(cmdline_arg ostree)" && test -z "$(cmdline_arg root)"; then
     cat >${UNIT_DIR}/sysroot.mount << 'EOF'
 [Unit]
 Before=initrd-root-fs.target
 After=coreos-rootflags.service
+ConditionPathExists=!/etc/cmdline.d/60kdumpip.conf
 [Mount]
 EnvironmentFile=/run/coreos-rootflags
 What=/dev/disk/by-label/root