pNFS/flexfiles: Set reasonable default retrans values for the data channel

Prior to this patch, the retrans value was set at 5, meaning that we
could see a maximum retransmission timeout value of more than 6 minutes.
That's a tad high for NFSv3 where the protocol does allow the server to
drop requests at any time.

Since this is a data channel, let's just set retrans to 0, and the default
timeout to 60s. The user can continue to adjust these defaults using the
dataserver_retrans and dataserver_timeo module parameters.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/flexfilelayout/flexfilelayoutdev.c

@@ -17,8 +17,8 @@
 
 #define NFSDBG_FACILITY		NFSDBG_PNFS_LD
 
-static unsigned int dataserver_timeo = NFS4_DEF_DS_TIMEO;
-static unsigned int dataserver_retrans = NFS4_DEF_DS_RETRANS;
+static unsigned int dataserver_timeo = NFS_DEF_TCP_RETRANS;
+static unsigned int dataserver_retrans;
 
 void nfs4_ff_layout_put_deviceid(struct nfs4_ff_layout_ds *mirror_ds)
 {