nfsd: fix version-setting regression on old kernels

nfsd: fix version-setting regression on old kernels

/proc/fs/nfsd/versions was extended to allow turning on/off minor
versions by echoing "+4.1" or "-4.1" to /proc/fs/nsfd/versions.

Unfortunately, pre-2.6.30 kernels just stop parsing at first non-digit,
so "-4.1" is interpreted as "-4".  If new nfs-utils (on old kernel)
writes "+2", "+3", "+4", then "-4.1", result therefore is to turn off
4.1.

Given that historical behavior, it may have been a mistake to extend the
interface the way we did; but at this point we're probably stuck with
it.  So, just reverse the order we write versions in.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Steve Dickson <steved@redhat.com>