nfsd41: destroy_session operation

Implement the destory_session operation confoming to
http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion1-26

[use sessionid_lock spin lock]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/include/linux/nfsd/xdr4.h b/include/linux/nfsd/xdr4.h
index 4861888..a0a2e83 100644
--- a/include/linux/nfsd/xdr4.h
+++ b/include/linux/nfsd/xdr4.h
@@ -395,7 +395,7 @@
 };
 
 struct nfsd4_destroy_session {
-	int	foo;	/* stub */
+	struct nfs4_sessionid	sessionid;
 };
 
 struct nfsd4_op {