build: fix build_clean.sh script to enable ibft

autotools build has/had a bug, where ibft test files would only be disted
if the ibft plugin was enabled.

Regardless of that, `build_clean.sh --release` is our suggested way to
create a release tarball. It should always enable the ibft plugin.

It didn't do so, due to a bug.

contrib/fedora/rpm/build_clean.sh

@@ -151,7 +151,7 @@ if [[ $NO_DIST != 1 ]]; then
         --with-libnm-glib \
         --enable-ifcfg-rh \
         --enable-ifupdown \
-        --enable-ibft \
+        --enable-config-plugin-ibft \
         --with-config-logging-backend-default=syslog \
         --with-libaudit=yes-disabled-by-default \
         --enable-polkit=yes \