Use "set -e" in the "tcp" system test

Use "set -e" in the "tcp" system test

Ensure any unexpected failure in the "tcp" system test causes it to be
immediately interrupted with an error to make the aforementioned test
more reliable.  Since the exit code for "expr 0 + 0" is 1, the status
variable needs to be updated using arithmetic expansion.

(cherry picked from commit 9841635b7f7adba64597247318f352c678082cfc)