Lucid SRU - UBUNTU: SAUCE: netns: Add quota for number of NET_NS instances.

[Tetsuo Handa]

Tim Gardner wrote:
> So, the first patch simply synchronously returns an error if the number 
> of network name spaces exceeds the specified maximum. This happens 
> within the context of the fork, the login process is aborted, and the 
> remote user is told to buzz off.

According to comment #24 of bug #790863, vsftpd in Lucid was updated to use
Debian's 10-remote-dos.patch 2.3.4-1 patch. So, we no longer need to worry
about vsftpd users, don't we?

I guess normal lxr containers will not start/terminate as frequent as ftp
clients. Thus, I think the first patch (give up immediately version) is fine.
Just setting initial quota value to 512 or so?