smb: client: transport: avoid reconnects triggered by pending task work

smb: client: transport: avoid reconnects triggered by pending task work

When io_uring is used in the same task as CIFS, there might be
unnecessary reconnects, causing issues in user-space applications
like QEMU with a log like:

> CIFS: VFS: \\10.10.100.81 Error -512 sending data on socket to server

Certain io_uring completions might be added to task_work with
notify_method being TWA_SIGNAL and thus TIF_NOTIFY_SIGNAL is set for
the task.

In __smb_send_rqst(), signals are masked before calling
smb_send_kvec(), but the masking does not apply to TIF_NOTIFY_SIGNAL.

If sk_stream_wait_memory() is reached via sock_sendmsg() while
TIF_NOTIFY_SIGNAL is set, signal_pending(current) will evaluate to
true there, and -EINTR will be propagated all the way from
sk_stream_wait_memory() to sock_sendmsg() in smb_send_kvec().
Afterwards, __smb_send_rqst() will see that not everything was written
and reconnect.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Steve French <stfrench@microsoft.com>