selftests/bpf: Add a specific dst port matching

After this patch:

 #102/1   flow_dissector_classification/ipv4:OK
 #102/2   flow_dissector_classification/ipv4_continue_dissect:OK
 #102/3   flow_dissector_classification/ipip:OK
 #102/4   flow_dissector_classification/gre:OK
 #102/5   flow_dissector_classification/port_range:OK
 #102/6   flow_dissector_classification/ipv6:OK
 #102     flow_dissector_classification:OK
 Summary: 1/6 PASSED, 0 SKIPPED, 0 FAILED

Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Link: https://patch.msgid.link/20250218043210.732959-5-xiyou.wangcong@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/bpf/prog_tests/flow_dissector_classification.c

@@ -542,15 +542,20 @@ static void detach_program(struct bpf_flow *skel, int prog_fd)
 
 static int set_port_drop(int pf, bool multi_port)
 {
+	char dst_port[16];
+
+	snprintf(dst_port, sizeof(dst_port), "%d", CFG_PORT_INNER);
+
 	SYS(fail, "tc qdisc add dev lo ingress");
-	SYS(fail_delete_qdisc, "tc filter add %s %s %s %s %s %s %s %s %s %s",
+	SYS(fail_delete_qdisc, "tc filter add %s %s %s %s %s %s %s %s %s %s %s %s",
 	    "dev lo",
 	    "parent FFFF:",
 	    "protocol", pf == PF_INET6 ? "ipv6" : "ip",
 	    "pref 1337",
 	    "flower",
 	    "ip_proto udp",
 	    "src_port", multi_port ? "8-10" : "9",
+	    "dst_port", dst_port,
 	    "action drop");
 	return 0;