net: core: check dev_valid_name in __dev_alloc_name

We currently only exclude non-sysfs-friendly names via
dev_get_valid_name; there doesn't seem to be a reason to allow such
names when we're called via dev_alloc_name.

This does duplicate the dev_valid_name check in the dev_get_valid_name()
case; we'll fix that shortly.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>