[PATCH 0 of 5] Remus/Libxl: Network buffering support

[rshriram@cs.ubc.ca]

This patch series adds support for network buffering in the Remus
codebase in libxl.

The series is organized as follows:
 1/5 - changes to autoconf scripts to check for libnl3. Add linker flags
       to libxl Makefile.

 2/5 - External script to setup/teardown network buffering using libnl3's CLI.
       This script will be invoked by libxl before starting Remus. The script's
       main job is to bring up an IFB device with plug qdisc attached to it.
       It then re-routes egress traffic from the guest's vif to the IFB device.

 3/5 - Libxl code to invoke the external setup script, followed by
       netlink related setup to obtain a handle on the output buffers attached
       to each vif.

 4/5 - Libxl interaction with network buffer module in the kernel via libnl3 API.

 5/5 - xl cmdline switch to explicitly enable network buffering when starting remus.


Few things to note:
a) Based on previous email discussions, the setup/teardown task has been moved to a 
   hotplug style shell script which can be customized as desired, instead of
   implementing it as C code inside libxl.

b) Libnl3 is not available on NetBSD. Nor is it available on CentOS (Linux).
   So I have made network buffering support an optional feature so that it can be
   disabled if desired.

c) NetBSD does not have libnl3. So I have put the setup script under
   tools/hotplug/Linux folder.

thanks
shriram