net: introduce qemu_get_queue()

To support multiqueue, the patch introduce a helper qemu_get_queue()
which is used to get the NetClientState of a device. The following patches would
refactor this helper to support multiqueue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/net/net.c b/net/net.c
index 2f0ab3a..b986161 100644
--- a/net/net.c
+++ b/net/net.c
@@ -234,6 +234,11 @@
     return nic;
 }
 
+NetClientState *qemu_get_queue(NICState *nic)
+{
+    return &nic->nc;
+}
+
 static void qemu_cleanup_net_client(NetClientState *nc)
 {
     QTAILQ_REMOVE(&net_clients, nc, next);