ttcn3-tcpdump-stop.sh: Don't use lsof

`lsof` isn't available in the docker image, use /proc fs instead to get
the shell type

Related: OS#5736
Change-Id: I38e132f49b0711d611d08b61c28b3092c991a191

ttcn3-tcpdump-stop.sh

@@ -25,7 +25,9 @@ kill_rm_pidfile() {
 date
 
 # -e only works/is required only in Bash; in dash/POSIX shells it isn't required and will be part of the output
-if (lsof -p $$ | grep -q /usr/bin/bash); then
+# SHELL environment variable doesn't always give name of current shell (e.g. for dash run inside bash...)
+SHELL_NAME="$(cat /proc/$$/cmdline |  tr -d '\0')"
+if [ "$SHELL_NAME" = "bash" ]; then
 	ESCAPE_OPT="-e"
 else
 	ESCAPE_OPT=""