Make NFS client use seq_list_xxx helpers

This includes /proc/fs/nfsfs/servers and /proc/fs/nfsfs/volumes entries.

Both need to show the header and use the list_head.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Acked-by: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>