net/virtio: fix interrupt handle leak

net/virtio: fix interrupt handle leak

Free memory of interrupt handle in virtio_user_dev_uninit() to
avoid memory leak.
when virtio user dev closes, memory of interrupt handle is not freed
that is allocated in virtio_user_fill_intr_handle().

Fixes: 3d4fb6fd2505 ("net/virtio-user: support Rx interrupt")
Cc: stable@dpdk.org
Signed-off-by: Gaoxiang Liu <liugaoxiang@huawei.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>