ip link: Remove unnecessary device checking

ip link: Remove unnecessary device checking

The real checking is performed later in iplink_modify(..) func which
checks device existence if NLM_F_CREATE flag is set.

Also it fixes the case when impossible to add veth link which was
caused by 9a02651a87 (ip: check for missing dev arg when doing VF rate)
because these devices are not exist yet.

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>