PNFS: set the default DS timeout to 60 seconds

The client should have 60 second default timeouts for DS operations, not 6
seconds.

NFS4_DEF_DS_TIMEO is used as "timeout in tenths of a second" in
nfs_init_timeout_values (and is not used anywhere else).
This matches up with the description of the module param dataserver_timeo.

Signed-off-by: Weston Andros Adamson <dros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>