selftests: rds: Make rds selftests TAP compliant

selftests: rds: Make rds selftests TAP compliant

This patch updates the rds selftests output to be TAP compliant.

Use ksft_pr() to mark debug output with a leading '# ' so that TAP
parsers treat it as commentary, and convert all informational print()
calls to use ksft_pr(). sys.exit(0) is changed to os._exit(0) to
avoid duplicate prints from the buffered TAP output. The console
output from the tcpdump subprocess is silenced, and the gcov console
output is redirected to a gcovr.log.

Finally adjust the exit path so that the hash check loop sets a
return code instead exiting directly. Then print the TAP results
and totals lines before exiting.

Signed-off-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260504054143.4027538-11-achender@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>