gvstream: don't request packet resend too early
gvstream: don't request packet resend too early

This change may need some adjustments. Before, we checked for packet
holes before the last received, and asked for resend immediately. Now,
we wait for at least the packet timeout before actually sending the
packet request, as we dont always receive packets in the increasing id
order. This should help to avoid unnecessary packet resend requests.

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