test: add test for trailing invalid byte at the end

(cherry picked from commit 894f441)
(cherry picked from commit c8c43dc)
(cherry picked from commit 6ec5484)

Author: yuwata

src/libsystemd-network/test-dhcp6-client.c

@@ -471,6 +471,8 @@ TEST(client_parse_message_issue_24002) {
                 0x20, 0x03, 0x00, 0xff, 0xaa, 0xbb, 0xcc, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* prefix */
                 /* Rapid commit */
                 0x00, 0x0e, 0x00, 0x00,
+                /* Trailing invalid byte at the end. See issue #28183. */
+                00,
         };
         static const uint8_t duid[] = {
                 0x00, 0x00, 0xab, 0x11, 0x5c, 0x6b, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff,