for #11257, h/t to @mna for the idea of resetting `token_update_tally`.
this is to cover scenarios where a host might be re-enrolling (eg: the
device has been wiped) but we don't know about it.
since `TokenUpdate` might be called multiple times during the lifecycle
of an MDM enrollment, we add a check on the value of
`nano_enrollments.token_update_tally`. For the scenarios described
above, the tally is still `> 0` even thought the host is enrolling for
the first time.
to mitigate this, we reset its value to 0 when we receive an
`Authenticate` message (which only happens only per enrollment)
I set the value to `0` because it's incremented to `current_value+1` by
nanomdm before calling our handler.
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