This helper function takes a remote IP address, and tries to
determine the dracut command line arguments ip= and ifname= that
will make this remote address reachable during boot.
Functionality was taken from the module-setup.sh scripts of 95iscsi and 95nfs,
cleaned up and fixed some issues in particular with statically configured
networks, where the old code would print the unsupported string
"$ifname:static".