DEV: flags/show-fd-to-flags: adapt to recent versions

DEV: flags/show-fd-to-flags: adapt to recent versions

The script hadn't been updated since it was introduced, and the
hard-coded field 12 doesn't match anymore (it's 16 now). Let's just
use "grep -o cflg..." to extract the desired part more flexibly.
This can be backported at least to 3.0, probably further, but it
will need to be tested prior to this. Better not bring it too far,
it's only used when debugging.