OK, I can see what's happening here. eth0 doesn't detect link-up until
after a few seconds, so when the vlan interface is opened immediately
after eth0 has been opened, it inherits the link-down state. Subsequently
the vlan interface is never properly activated and are thus unable to
transmit any packets.

dev->state bits are not supposed to be manipulated directly. Something
similar is probably needed for the netif_device_present() bit, although
I don't know how this is meant to work for a virtual device.
Signed-off-by: David S. Miller <davem@davemloft.net>