qa/live: fail the dpdk test when no packets are captured

When Suricata exits during startup it never writes a stats event, so jq
returns an empty string and the test aborted the comparison with
"unary operator expected".
Quote the value and compare it against the expected outcome, so an empty
result fails the same way a false one does.

qa/live/dpdk.sh

@@ -42,7 +42,7 @@ sleep 15
 
 # check stats and alerts
 STATSCHECK=$(jq -c 'select(.event_type == "stats")' ./eve.json | tail -n1 | jq '.stats.capture.packets > 0')
-if [ $STATSCHECK = false ]; then
+if [ "$STATSCHECK" != true ]; then
     echo "ERROR no packets captured"
     RES=1
 fi
@@ -59,7 +59,7 @@ sleep 15
 
 # check stats and alerts
 STATSCHECK=$(jq -c 'select(.event_type == "stats")' ./eve.json | tail -n1 | jq '.stats.capture.packets > 0')
-if [ $STATSCHECK = false ]; then
+if [ "$STATSCHECK" != true ]; then
     echo "ERROR no packets captured"
     RES=1
 fi