nfsd: Don't fail OP_SETCLIENTID when there are too many clients.

nfsd: Don't fail OP_SETCLIENTID when there are too many clients.

Failing OP_SETCLIENTID or OP_EXCHANGE_ID should only happen if there is
memory allocation failure.  Putting a hard limit on the number of
clients is not really helpful as it will either happen too early and
prevent clients that the server can easily handle, or too late and
allow clients when the server is swamped.

The calculated limit is still useful for expiring courtesy clients where
there are "too many" clients, but it shouldn't prevent the creation of
active clients.

Testing of lots of clients against small-mem servers reports repeated
NFS4ERR_DELAY responses which doesn't seem helpful.  There may have been
reports of similar problems in production use.

Also remove an outdated comment - we do use a slab cache.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>