tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG

These records connect through source-stated identifiers. Shared identifiers or dates alone do not establish shared exposure, root cause or applicability.

CVE-2026-31662 · Microsoft / collected KEV context

cve-program · CVE-2026-31662

• https://git.kernel.org/stable/c/a7db57ccca21f5801609065473c89a38229ecb92
• https://git.kernel.org/stable/c/36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412
• https://git.kernel.org/stable/c/575faea557f1a184a5f09661bd47ebd3ef3769f8
• https://git.kernel.org/stable/c/3bcf7aca63f0bcd679ae28e9b99823c608e59ce3
• https://git.kernel.org/stable/c/a2ea1ef0167d7a84730638d05c20ccdc421b14b6
• https://git.kernel.org/stable/c/1b6f13f626665cac67ba5a012765427680518711
• https://git.kernel.org/stable/c/e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682
• https://git.kernel.org/stable/c/48a5fe38772b6f039522469ee6131a67838221a8

No related operational record is retained in the current change model.