tools/virtio: Ignore virtio-trace/trace-agent

since commit 108fc82("tools: Add guest trace agent as a user tool")
introduce virtio-trace/trace-agent, it should be ignored in the git tree.

Signed-off-by: Rong Tao <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>

Author: Rtoax

tools/virtio/.gitignore

@@ -2,3 +2,4 @@
 *.d
 virtio_test
 vringh_test
+virtio-trace/trace-agent