NFS: Fix nfsstat breakage due to LOOKUPP

The LOOKUPP operation was inserted into the nfs4_procedures array
rather than being appended, which put /proc/net/rpc/nfs out of
whack, and broke the nfsstat utility.
Fix by moving the LOOKUPP operation to the end of the array, and
by ensuring that it keeps the same length whether or not NFSV4.1
and NFSv4.2 are compiled in.

Fixes: 5b5faaf6 ("nfs4: add NFSv4 LOOKUPP handlers")
Cc: stable@vger.kernel.org # v4.13+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>