Ensure that we fix up the missing fields in the nfs_mount_data with
sane defaults for older versions of mount, and return errors in the
cases where we cannot.
Convert a bunch of annoying warnings into dprintks()
Return -EPROTONOSUPPORT rather than EIO if mount() tries to set NFSv3
without it actually being compiled in.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>