net/virtio-user: fix link status

net/virtio-user: fix link status

Previously, we miss to set intr_handle->fd which will be used as
target file for epoll to check LSC.

As a result, stdin (0) is used and intr thread keeps busy whenever
data comes from stdin.

To fix this, we use vhostfd as the target file for epoll to check
the link status change events. And we move intr_handle initialization
after vhost backend settup to make sure vhostfd is initialized.

Fixes: 35c4f8554833 ("net/virtio-user: support to report net status")

Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>