tap: fix a memory leak

Close fd before returning.

Buglink: https://bugs.launchpad.net/qemu/+bug/1904486

Signed-off-by: yuanjungong <ruc_gongyuanjun@163.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/tap.c

@@ -817,6 +817,7 @@ int net_init_tap(const Netdev *netdev, const char *name,
         if (ret < 0) {
             error_setg_errno(errp, -ret, "%s: Can't use file descriptor %d",
                              name, fd);
+            close(fd);
             return -1;
         }
 
@@ -831,6 +832,7 @@ int net_init_tap(const Netdev *netdev, const char *name,
                          vhostfdname, vnet_hdr, fd, &err);
         if (err) {
             error_propagate(errp, err);
+            close(fd);
             return -1;
         }
     } else if (tap->has_fds) {