This fixes a regression caused by the following commit,
which prevents the file flag from being updated.
```
commit 28860b5242dd5efd86b5da8a089e5d898cd8a9a1
Author: chao.an <anchao@xiaomi.com>
Date: Sat Mar 19 14:47:37 2022 +0800
net/netdev: fix switch case missing break
Signed-off-by: chao.an <anchao@xiaomi.com>
```
Note: some applications like mbedtls uses F_GETFL to confirm
the nonblock-ness of the socket. This is critical for such
applications.
bc0ca51243