pc-bios/s390-ccw: Increase virtio timeout to 30 seconds

The current timeout is set to only three seconds - and considering that
vring_wait_reply() or rather get_second() is not doing any rounding,
the real timeout is likely rather 2 seconds in most cases. When the
host is really badly loaded, it's possible that we hit this timeout by
mistake; it's even more likely if we run the guest in TCG mode instead
of KVM.

So let's increase the timeout to 30 seconds instead to ease this situation
(30 seconds is also the timeout that is used by the Linux SCSI subsystem
for example, so this seems to be a sane value for block IO timeout).

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1549079


Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1522316251-16399-1-git-send-email-thuth@redhat.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
[CH: tweaked commit message]
Signed-off-by: Cornelia Huck <cohuck@redhat.com>