ikev1 xauth but no modecfg; client misconfigured (missing subnet=)

- establish using main mode
- server authenticates client using XAUTH

MODE_CFG is skipped

- misconfigured client then initiates Quick Mode proposing HOST
  address as client

it gets rejected

This illustrates historic behaviour where, a missing subnet=
assumes transport and tries to use host addresses.

Note: to get this behaviour modecfgserver=no modecfgclient=no

modeconfigpull=yes is needed, see github/1961.

For background see github/1955
