vrf: use RCU protection in l3mdev_l3_out()

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

CVE-2025-21791 · Microsoft / collected KEV context

cve-program · CVE-2025-21791

• https://git.kernel.org/stable/c/6ccaa5797f5362a2aad6baa6ddaf4715ac2dd51e
• https://git.kernel.org/stable/c/20a3489b396764cc9376e32a9172bee26a89dc3b
• https://git.kernel.org/stable/c/5bb4228c32261d06e4fbece37ec3828bcc005b6b
• https://git.kernel.org/stable/c/c7574740be8ce68a57d0aece24987b9be2114c3c
• https://git.kernel.org/stable/c/c40cb5c03e37552d6eff963187109e2c3f78ef6f
• https://git.kernel.org/stable/c/022cac1c693add610ae76ede03adf4d9d5a2cf21
• https://git.kernel.org/stable/c/7b81425b517accefd46bee854d94954f5c57e019
• https://git.kernel.org/stable/c/6d0ce46a93135d96b7fa075a94a88fe0da8e8773

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