For rxq interrupt, the device (backend driver) will notify driver
through callfd. Each virtqueue has a callfd. To keep compatible
with the existing framework, we will give these callfds to
interrupt thread for listening for interrupts.
Before that, we need to allocate intr_handle, and fill callfds
into it so that driver can use it to set up rxq interrupt mode.
Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
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