ttcn3-tcpdump*.sh: Log stderr separately to file

The old output is preserved, too, in order to ensure
compatibility with expectations regarding legacy behavior.

Related: OS#5736

Change-Id: Ia92ff32c8ce09ab7805c5509837ec88fa4b864c5
diff --git a/ttcn3-tcpdump-stop.sh b/ttcn3-tcpdump-stop.sh
index 6796612..829ed2b 100755
--- a/ttcn3-tcpdump-stop.sh
+++ b/ttcn3-tcpdump-stop.sh
@@ -2,6 +2,7 @@
 
 PIDFILE_PCAP=/tmp/pcap.pid
 PIDFILE_NETCAT=/tmp/netcat.pid
+FIFO=/tmp/cmderr
 TESTCASE=$1
 VERDICT="$2"
 
@@ -68,5 +69,6 @@
 
 kill_rm_pidfile "$PIDFILE_PCAP"
 kill_rm_pidfile "$PIDFILE_NETCAT"
+rm $FIFO
 
 gzip -f "$TTCN3_PCAP_PATH/$TESTCASE.pcap"