This allows the GSM connection to Just Work most of the time, as in:
"nmcli d connect ttyUSB0".

After 1.20.0 is released, merge it back into master so that
1.20.0 is part of the history of master. That means,
  $ git log --first-parent master
will also traverse 1.20.0 and 1.20-rc*.

Also bump the micro version to 1.21.1-dev to indicate that this is
after 1.20.0 is out.

The functionality of the ibft settings plugin is now handled by
nm-initrd-generator. There is no need for it anymore, drop it.

Note that ibft called iscsiadm, which requires CAP_SYS_ADMIN to work
([1]). We really want to drop this capability, so the current solution
of a settings plugin (as it is implemented) is wrong. The solution
instead is nm-initrd-generator.

Also, on Fedora the ibft was disabled and probably on most other
distributions as well. This was only used on RHEL.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1371201#c7