NFS/pnfs: Separate NFSv3 DS and MDS traffic

If a NFSv3 server is being used as both a DS and as a regular NFSv3 server,
we may want to keep the IO traffic on a separate TCP connection, since
it will typically have very different timeout characteristics.

This patch therefore sets up a flag to separate the two modes of operation
for the nfs_client.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

include/linux/nfs_fs_sb.h

@@ -46,6 +46,7 @@ struct nfs_client {
 #define NFS_CS_NO_RETRANS_TIMEOUT	4	/* - Disable retransmit timeouts */
 #define NFS_CS_TSM_POSSIBLE	5		/* - Maybe state migration */
 #define NFS_CS_NOPING		6		/* - don't ping on connect */
+#define NFS_CS_DS		7		/* - Server is a DS */
 	struct sockaddr_storage	cl_addr;	/* server identifier */
 	size_t			cl_addrlen;
 	char *			cl_hostname;	/* hostname of server */