Correctly probe mount v2

Correctly probe mount v2

When following a list of mount versions to probe -
e.g. probe_mnt1_first or probe_mnt3_first - probe_both will first
probe the appropriate NFS version and then, if that succeeds, probe
the actual mount version.  However instead of probing the target mount
version, it probes the "most appropriate" mount version for the given NFS version.
This results in it probing:
  NFSv2, MOUNTv1
twice rather than
  NFSv2, MOUNTv1
  NFSv2, MOUNTv2

as would be more correct.

This patch removes the "choose most correct" step and just use the
current mouint version for the probe_vers array.