selftests/tls: close the socket with open record

Add test which sends some data with MSG_MORE and then
closes the socket (never calling send without MSG_MORE).
This should make sure we clean up open records correctly.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>