DAFS: Do not let VScheduleSalvage_r free vp

DAFS: Do not let VScheduleSalvage_r free vp

In VScheduleSalvage_r, we were calling VCancelReservation_r, which has
the possibility of free'ing vp. Since we still use vp after doing this
(and since we're already inside VCancelReservation_r to begin with),
we must not free vp. Instead, just decrement nWaiters without
triggering any of the dtor code in VCancelReservation_r. This is safe
as long as all VScheduleSalvage_r callers ensure that they check to
free the vp if necessary, which they all do.

Thanks to Derrick Brashear.

Change-Id: Iebdbdf47c6307cd7c036b88ad4dbc25bc7a3279a
Reviewed-on: http://gerrit.openafs.org/3272
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>