fix inverted logic in overprovision parameter
fix inverted logic in overprovision parameter

we want to set thread affinity to *false* if overprovisioned.
Current logic is inverted.

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>
Message-Id: <1485452698-32221-1-git-send-email-7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

scylladb/seastar,syuu1228/seastar,cloudius-systems/seastar,dreamsxin/seastar,dreamsxin/seastar,syuu1228/seastar,cloudius-systems/seastar,cloudius-systems/seastar,scylladb/seastar,avikivity/seastar,dreamsxin/seastar,avikivity/seastar,syuu1228/seastar,scylladb/seastar,avikivity/seastar