qemu-option: qemu_opts_from_qdict(): use error_set()

do_device_add() and do_netdev_add() call qerror_report_err() to maintain
their QError semantics.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-By: Laszlo Ersek <lersek@redhat.com>
diff --git a/net.c b/net.c
index f5d9cc7..246209f 100644
--- a/net.c
+++ b/net.c
@@ -1237,11 +1237,14 @@
 
 int do_netdev_add(Monitor *mon, const QDict *qdict, QObject **ret_data)
 {
+    Error *local_err = NULL;
     QemuOpts *opts;
     int res;
 
-    opts = qemu_opts_from_qdict(qemu_find_opts("netdev"), qdict);
+    opts = qemu_opts_from_qdict(qemu_find_opts("netdev"), qdict, &local_err);
     if (!opts) {
+        qerror_report_err(local_err);
+        error_free(local_err);
         return -1;
     }