shellcheck: linux-tor-prio.sh issues

In linux-tor-prio.sh line 98:
MTU=1500
^-- SC2034: MTU appears unused. Verify use (or export if used externally).


In linux-tor-prio.sh line 108:
BDP=$(expr $RTT_LATENCY \* $RATE_UP / $AVG_PKT)
      ^-- SC2003: expr is antiquated. Consider rewriting this using $((..)), ${} or [[ ]].


In linux-tor-prio.sh line 113:
BDP=$(expr $BDP / 4)
      ^-- SC2003: expr is antiquated. Consider rewriting this using $((..)), ${} or [[ ]].
           ^-- SC2086: Double quote to prevent globbing and word splitting.


In linux-tor-prio.sh line 151:
ip link set dev $DEV qlen $BDP
                          ^-- SC2086: Double quote to prevent globbing and word splitting.


In linux-tor-prio.sh line 161:
tc class add dev $DEV parent 1:1 classid 1:20 htb rate $(expr $RATE_UP - $RATE_UP_TOR)kbit ceil ${RATE_UP}kbit prio 0
                                                       ^-- SC2046: Quote this to prevent word splitting.
                                                         ^-- SC2003: expr is antiquated. Consider rewriting this using $((..)), ${} or [[ ]].


In linux-tor-prio.sh line 162:
tc class add dev $DEV parent 1:1 classid 1:21 htb rate $[$RATE_UP_TOR]kbit ceil ${RATE_UP_TOR_CEIL}kbit prio 10
                                                       ^-- SC2007: Use $((..)) instead of deprecated $[..]


In linux-tor-prio.sh line 165:
tc qdisc add dev $DEV parent 1:20 handle 20: pfifo limit $BDP
                                                         ^-- SC2086: Double quote to prevent globbing and word splitting.


In linux-tor-prio.sh line 166:
tc qdisc add dev $DEV parent 1:21 handle 21: pfifo limit $BDP
                                                         ^-- SC2086: Double quote to prevent globbing and word splitting.


In linux-tor-prio.sh line 179:
if [ ""$TOR_IP == "" ]
       ^-- SC2086: Double quote to prevent globbing and word splitting.


In linux-tor-prio.sh line 182:
	iptables -t mangle -A TORSHAPER-OUT -m owner --uid-owner $TOR_UID -j MARK --set-mark 21
                                                                 ^-- SC2086: Double quote to prevent globbing and word splitting.


In linux-tor-prio.sh line 185:
	iptables -t mangle -A TORSHAPER-OUT -s $TOR_IP -j MARK --set-mark 21
                                               ^-- SC2086: Double quote to prevent globbing and word splitting.