staging/lustre/mdc: move mdc-specific procfs files to sysfs

This moves max_rpcs_in_flight and max_pages_per_rpc to
/proc/fs/lustre/mdc/.../

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>