protocoldetector: Avoid unneeded syscalls

When cleaning up non-responsive connections, it is enough to get the
current time once, and it also make the code little bit more clear.

Change-Id: I57ca0e40bd32fc0848eddeeb77a499be6fd01ba1
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34331
Reviewed-by: Piotr Kliczewski <piotr.kliczewski@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>