io_uring/net: commit partial buffers on retry

In the Linux kernel, the following vulnerability has been resolved:

io_uring/net: commit partial buffers on retry

Ring provided buffers are potentially only valid within the single execution context in which they were acquired. io_uring deals with this and invalidates them on retry. But on the networking side, if MSG_WAITALL is set, or if the socket is of the streaming type and too little was processed, then it will hang on to the buffer rather than recycle or commit it. This is problematic for two reasons:

1) If someone unregisters the provided buffer ring before a later retry, then the req->buf_list will no longer be valid.

2) If multiple sockers are using the same buffer group, then multiple receives can consume the same memory. This can cause data corruption in the application, as either receive could land in the same userspace buffer.

Fix this by disallowing partial retries from pinning a provided buffer across multiple executions, if ring provided buffers are used.