net: use dev->name in netdev_pr* when it's available

netdev_name() returns dev->name only when the net_device is in
NETREG_REGISTERED state.

However, dev->name is always populated on creation, so we can easily use
it.

There are two cases when there's no real name - when it's an empty string
or when the name is in form of "eth%d", then netdev_name() returns "unnamed
net_device".

CC: "David S. Miller" <davem@davemloft.net>
CC: Tom Gundersen <teg@jklm.no>
Signed-off-by: Veaceslav Falico <vfalico@gmail.com>
Acked-by: Tom Gundersen <teg@jklm.no>
Signed-off-by: David S. Miller <davem@davemloft.net>