vfio/pci: Fix unsigned comparison overflow

vfio/pci: Fix unsigned comparison overflow

Signed versus unsigned comparisons are implicitly cast to unsigned,
which result in a couple possible overflows.  For instance (start +
count) might overflow and wrap, getting through our validation test.
Also when unwinding setup, -1 being compared as unsigned doesn't
produce the intended stop condition.  Fix both of these and also fix
vfio_msi_set_vector_signal() to validate parameters before using the
vector index, though none of the callers should pass bad indexes
anymore.

OraBug: 26223261
Reported-by: Eric Auger <eric.auger@linaro.org>
Reviewed-by: Eric Auger <eric.auger@linaro.org>
Tested-by: Eric Auger <eric.auger@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
(cherry picked from commit b95d9305e8cb8d432ca02da1b759fef59bc50ace)
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>