[pnfs] couple 2.6.23 server patches

[dean hildebrand]

I'm going to send out two patches that apply against the 2.6.23 server.
Ricardo, are you applying these or how are we handling 2.6.23?

1. Use a helper function to help differentiate between a
server exporting a file system that doesn't support pNFS
and a server exporting a file system that supports a
different layout type.
2. Remove some unnecessary and outdated comments.

Dean