net/core: use netdev name in warning if no parent

A recent flaw in the netdev feature setting resulted in warnings
like this one from VLAN interfaces:

 WARNING: CPU: 1 PID: 4975 at net/core/dev.c:2419 skb_warn_bad_offload+0xbc/0xcb()
 : caps=(0x00000000001b5820, 0x00000000001b5829) len=2782 data_len=0 gso_size=1348 gso_type=16 ip_summed=3

The ":" is supposed to be preceded by a driver name, but in this
case it is an empty string since the device has no parent.

There are many types of network devices without a parent. The
anonymous warnings for these devices can be hard to debug.  Log
the network device name instead in these cases to assist further
debugging.

This is mostly similar to how __netdev_printk() handles orphan
devices.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>