NFS: Ensure that the nfs_client 'net' field is always set

Currently, the nfs_parsed_mount_data->net field is initialised in
the nfs_parse_mount_options() function, which means that it only
gets set if we're using text based mounts. The legacy binary
mount interface is therefore broken.

Fix is to initialise the ->net field in nfs_alloc_parsed_mount_data.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>