ip: allow using a device "help" (or a prefix thereof)

Device names that match "help" or a prefix thereof should be allowed anywhere
a device name can be used. Note that a suitable keyword ("dev" or "name", the
latter for "ip tunnel") has to be used in these cases to resolve ambiguities.

Signed-off-by: Christoph Schulz <develop@kristov.de>
Reported-by: Leonhard Preis <leonhard@pre.is>
Reported-by: Wilhelm Wijkander <lists@0x5e.se>
4 files changed