regression: unregister_netdev() unusably slow

[Benjamin LaHaise <bcrl@lhnet.ca>]

Hi folks,

I just ran a few L2TP tests against 2.6.30-rc7, and it looks like network 
device deletion has become unusably slow.  At least in 2.6.27.10, deleting 
1000 network interfaces takes less than 2 seconds of real time.  The same 
test run under 2.6.30-rc7 is taking hundreds of seconds to delete 1000 
interfaces at a rate of about 5 per second.  The interfaces all share the 
same local ip address, but each have a single route to a unique client 
ip address.

This is a fairly reasonable use-case, as a single L2TP daemon can be 
terminating thousands of client connections on a single tunnel, and a 
tunnel flap will require tearing down all these interfaces.  I'll work on 
bisecting it, but if someone has any ideas of the source, I'd appreciate 
hearing about it.

		-ben