scsi: Specify the xfer direction for UNMAP and ATA_PASSTHROUGH commands

scsi_cmd_xfer_mode() is used to specify the xfer direction for SCSI
commands that come in from the guest.  If the direction is set incorrectly
this will eventually cause QEMU to kernel-panic the guest.

Add UNMAP and ATAPASSTHROUGH as commands that send data to the device.

Without this change, recent kernels will send both UNMAP as well
as ATAPASSTHROUGH commands to any /dev/sg* device, which due to the
incorrect xfer direction very quickly causes the guest kernel to crash.

Example causing a crash without the patch applied:

./x86_64-softmmu/qemu-system-x86_64 -m 1024 -enable-kvm -cdrom linuxmint-12-gnome-dvd-64bit.iso -drive file=/dev/sg4,if=scsi,bus=0,unit=6
Signed-off-by: NRonnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/scsi-bus.c

@@ -940,6 +940,7 @@ static void scsi_cmd_xfer_mode(SCSICommand *cmd)
     case WRITE_LONG_10:
     case WRITE_SAME_10:
     case WRITE_SAME_16:
+    case UNMAP:
     case SEARCH_HIGH_12:
     case SEARCH_EQUAL_12:
     case SEARCH_LOW_12:
@@ -949,6 +950,7 @@ static void scsi_cmd_xfer_mode(SCSICommand *cmd)
     case SEND_DVD_STRUCTURE:
     case PERSISTENT_RESERVE_OUT:
     case MAINTENANCE_OUT:
+    case ATA_PASSTHROUGH:
         cmd->mode = SCSI_XFER_TO_DEV;
         break;
     default: