Add warning about GRO and Neutron routers

Generic Receive Offload appears to be enabled by default on recent Ubuntu
kernels. It can have a significant impact on download performance when
enabled on a Neutron router interface. This patch warns users about that.

Change-Id: I3d3a560b1db55aabd901f27ad5c7bd5777b300da
Closes-bug: 1252900
rst-xml-conversion revisited

we likely will be using most of the developer reference material in
the developer training guide. there is good tidbits of information like
what is patched here. as it gets included, some reformating will get pushed
back into the cinder project. like the architecture asc art will get either
converted into a diagram or add a flag for an xml programlisting tag. rst files
in the devref source, but not converted to xml will get patched in cinder
for update or removal.

implements blueprint rst-xml-conversion

Change-Id: Ib4a577a77d0d19e1864860c6940a46cbb11b2028
Merge "rst-xml-conversion revisited"