fix(cpworker): walk QinQ tag stacks in custom req_pattern direction detection - #287

Problem

With a custom req_pattern, req_pattern_judge_pkt_direction() parses the IP/port of each frame. The parser followed only 0x8100 tags. A frame whose tag stack contains an 802.1ad (0x88a8) or 0x9100/0x9200 tag never reached the IP layer, was judged PKT_DIR_UNKNOWN, and every output dropped it as a direction drop. With a custom pattern, all QinQ traffic on the interface was lost.

parse_packet (packet_split.c) and output_zmq.c already accept all four TPIDs.

Changes

• vlan.h: add is_vlan_ethertype() for the four tag TPIDs.
• req_pattern.c: extract_ipport_from_ether_layer skips the whole tag stack in a loop, bounded by caplen, then dispatches to IPv4/IPv6. extract_ipport_from_vlan_layer is removed: it recursed once per tag, so its depth was bounded only by caplen.
• output_zmq.c: use is_vlan_ethertype() in the existing tag walk (no behaviour change).
• The VXLAN inner frame goes through the same Ethernet parser, so QinQ inside VXLAN is also fixed.

packet_split.c keeps its own four-way check for now.

Tests

New tests/unit/req_pattern.c (14 tests). Before the fix, the 7 QinQ cases failed and the controls passed.

• Request/reply direction through: untagged, 802.1Q, 802.1Q×2, 0x88a8+0x8100, 0x9100+0x8100, 0x9200+0x8100, single 0x88a8, a 4-tag mixed stack
• QinQ + IPv6; QinQ inside VXLAN
• Tag stack or IP header cut by caplen → unknown; a frame made only of tags → unknown

Unit tests 9/9 and the integration suite pass (Ubuntu 24.04).

Fixes #270