Add missing truncated HMAC test for TLS

The case 'Client disabled, Server enabled' was missing.
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 0082f6a..8697db9 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -860,6 +860,15 @@
             -S "dumping 'expected mac' (10 bytes)"
 
 requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
+run_test    "Truncated HMAC: client disabled, server enabled" \
+            "$P_SRV debug_level=4 trunc_hmac=1" \
+            "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA \
+             trunc_hmac=0" \
+            0 \
+            -s "dumping 'expected mac' (20 bytes)" \
+            -S "dumping 'expected mac' (10 bytes)"
+
+requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
 run_test    "Truncated HMAC: client enabled, server enabled" \
             "$P_SRV debug_level=4 trunc_hmac=1" \
             "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA \