MFC fixes for uninitialized kernel stack variables in sys/cam or do direct fix for pvscsi driver

Hi Warner,

Recently I upgraded some ESXi vms from 13.3 to 13.4 and noticed weird report for sas speed.
The boot console has the following,

```
da0 at pvscsi0 bus 0 scbus2 target 0 lun 0
da0: <VMware Virtual disk 2.0> Fixed Direct Access SPC-4 SCSI device
da0: 4294967.295MB/s transfers
```
But camcontrol report the correct value,
```
# camcontrol inquiry da0 -R
pass1: 750.000MB/s transfers, Command Queueing Enabled
```

The `4294967.295MB` is actually 0xffff_ffff or -1 but I do not see any logic set those values.

Finally I managed to get the stack trace,
```
_scsi_announce_periph
scsi_announce_periph_sbuf
xpt_announce_periph_sbuf
dadone_proberc
xpt_done_process
xpt_done_td
fork_exit
fork_trampoline
```

and noticed that the last param `cts` of `_scsi_announce_periph(struct cam_periph *periph, u_int *speed, u_int *freq, struct ccb_trans_settings *cts)`
is from kernel stack and is not properly initialized, latter I found some commits related to this,

076686fe0703 cam: make sure to clear CCBs allocated on the stack
ec5325dbca62 cam: make sure to clear even more CCBs allocated on the stack
0f206cc91279 cam: add missing zeroing of a stack-allocated CCB.
616a676a0535 cam: clear stack-allocated CCB in the target layer

I applied them to stable/13, rebuild and reboot, now the speed of da0 is reported correctly. I also tried to patch the pvscsi driver with few lines and
it also works as intended.

```
--- a/sys/dev/vmware/pvscsi/pvscsi.c
+++ b/sys/dev/vmware/pvscsi/pvscsi.c
@@ -1444,6 +1444,10 @@ pvscsi_action(struct cam_sim *sim, union ccb *ccb)
                cts->proto_specific.scsi.flags = CTS_SCSI_FLAGS_TAG_ENB;
                cts->proto_specific.scsi.valid = CTS_SCSI_VALID_TQ;
 
+               /* Prefer connection speed over sas port speed */
+               /* cts->xport_specific.sas.bitrate = 0; */
+               cts->xport_specific.sas.valid = 0;
+
                ccb_h->status = CAM_REQ_CMP;
                xpt_done(ccb);
```

Things come clear and I know why this weird speed happens, now it is time to decide how to fix it.

Fixing the consumer of cam, aka pvscsi driver, is quite simple and promising. I did a quick search it appears other consumers set `cts->xport_specific.sas.valid` correctly. It does not convince me as I'm quite new to cam subsystem.

Which one do you prefer, MFC commits to stable/13, or do direct fix for pvscsi driver to stable/13 ?

Best regards,
Zhenlei