Add TUNSETCARRIER ioctl, then we may change the carrier state of TUN dynamically. Note that we don't need an ioctl for getting carrier, it can be done by SIOCGIFFLAGS already.
Ref: https://github.com/torvalds/linux/blob/v6.10/drivers/net/tun.c#L3374-L3380
Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>