vdev_id: implement slot numbering by port id

With HPE hardware and hpsa-driven SAS adapters, only a single phy is
reported, but no individual per-port phys (ie. no phy* entry below
port_dir), which breaks topology detection in the current sas_handler
code. Instead, slot information can be derived directly from the port
number. This change implements a new slot keyword "port" similar to
"id" and "lun", and assumes a default phy/port of 0 if no individual
phy entry can be found. It allows to use the "sas_direct" topology with
current HPE Dxxxx and Apollo 45xx JBODs.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Daniel Kobras <d.kobras@science-computing.de>
Closes #6484

cmd/vdev_id/vdev_id

@@ -237,7 +237,7 @@ sas_handler() {
 
 	PHY=`ls -d $port_dir/phy* 2>/dev/null | head -1 | awk -F: '{print $NF}'`
 	if [ -z "$PHY" ] ; then
-		return
+		PHY=0
 	fi
 	PORT=$(( $PHY / $PHYS_PER_PORT ))
 
@@ -262,6 +262,10 @@ sas_handler() {
 	"phy")
 		SLOT=`cat $end_device_dir/phy_identifier 2>/dev/null`
 		;;
+	"port")
+		d=$(eval echo \${$i})
+		SLOT=`echo $d | sed -e 's/^.*://'`
+		;;
 	"id")
 		i=$(($i + 1))
 		d=$(eval echo \${$i})