NFSv4.1: Set the maximum slot table size to 1024 slots

This means that we end up statically allocating 128 bytes for the
bitmap on each slot table.
For a server that supports 1MB write and read I/O sizes this means
that we can completely fill the maximum 1GB TCP send/receive
windows.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>