nut: initscripts hotplug: Fix many small semantic issues

Small but important tweaks to fix the operation of the nut initscripts
and hotplug scripts.  All hail shellcheck and proofreading and
dogfooding.

Signed-off-by: Daniel F. Dickinson <cshored@thecshore.com>

net/nut/files/nut_serial.hotplug

@@ -2,20 +2,33 @@
 
 nut_serial() {
 	local cfg="$cfg"
-	config_get runas upsd runas "nut"
+	local runas enable_usb_serial port
 	config_get_bool enable_usb_serial "$cfg" enable_usb_serial 0
-}
+	config_get port "$cfg" port
+	config_get runas "$cfg" runas "nut"
 
-[ "$ACTION" = "add" ] && [ -n "$DEVNAME" ] && [ -z "${DEVNAME%ttyUSB*}" ] && {
-	config load nut_server
-	config_foreach nut_serial driver
-
-	[ -z "$RUNAS" ] && {
-		RUNAS="$runas"
-	}
+	[ -z "$runas" ] && config_get runas upsd runas "nut"
 
 	[ "$enable_usb_serial" -eq 1 ] && {
-			chown "${RUNAS:-nut}" /dev/$DEVNAME
-			chmod g+rw /dev/$DEVNAME
+		# If port is specified only change tty's matching port
+		if [ -n "$port" ] && [ "$port" != /dev/"$DEVNAME" ]; then
+			return 0
+		fi
+		[ -n "$runas" ] && chgrp "$(id -gn "${runas}")" /dev/"$DEVNAME"
+		chmod g+rw /dev/"$DEVNAME"
 	}
 }
+
+nut_on_hotplug_add() {
+	. "${IPKG_INSTROOT}"/lib/functions.sh
+
+	config load nut_server
+	config_foreach nut_serial driver
+}
+
+[ "$ACTION" = "add" ] && [ -n "$DEVNAME" ] && {
+	# On add of a serial port with name ttyUSB*
+	[ -z "${DEVNAME%ttyUSB*}" ] && nut_on_hutplug_add
+	# On add of a serial port with name ttyAMA*
+	[ -z "${DEVNAME%ttyAMA*}" ] && nut_on_hutplug_add
+}