This patch fixes a regression in 2.6.19 in which the use of multiple
krb5 mounts against the same NFS server may result in an Oops on
unmount. The Oops is due to the fact that multiple NFS krb5 clients may
end up inadvertently sharing the same rpc_pipefs upcall pipe. The first
client to 'umount' will unlink that shared pipe, causing an Oops.

The solution is to give each client their own upcall pipe. This fix has
been in mainline since 2.6.20-rc1.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
[chrisw: backport to 2.6.19.2]
Signed-off-by: Chris Wright <chrisw@sous-sol.org>