vduse: relicense under GPL-2.0 OR BSD-3-Clause

Dual-license the vduse kernel header file to dual
GPL-2.0 OR BSD-3-Clause license to make it possible
to ship it with DPDK (under BSD-3-Clause) for older
distros.

Signed-off-by: Yongji Xie <xieyongji@bytedance.com>
Message-Id: <20241119074238.38299-1-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>