Merge branch 'vsock-introduce-siocinq-ioctl-support'

Xuewei Niu says:

====================
vsock: Introduce SIOCINQ ioctl support

Introduce SIOCINQ ioctl support for vsock, indicating the length of unread
bytes.

Similar with SIOCOUTQ ioctl, the information is transport-dependent.

The first patch adds SIOCINQ ioctl support in AF_VSOCK.

Thanks to @dexuan, the second patch is to fix the issue where hyper-v
`hvs_stream_has_data()` doesn't return the readable bytes.

The third patch wraps the ioctl into `ioctl_int()`, which implements a
retry mechanism to prevent immediate failure.

The last one adds two test cases to check the functionality. The changes
have been tested, and the results are as expected.
====================

Link: https://patch.msgid.link/20250708-siocinq-v6-0-3775f9a9e359@antgroup.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>