staging: lustre: ptlrpc: do not switch out-of-date context

When trying to replace a dead sec context with a new one, we must
ensure the new context is already up-to-date.
If it is not the case, just return from sptlrpc_req_replace_dead_ctx()
and come later when the new context has been updated.

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6536
Reviewed-on: http://review.whamcloud.com/15708


Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>