CVE-2026-98624: netfilter: nfnetlink_queue: hold nfnl mutex in event notifier

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nfnetlinkqueue: hold nfnl mutex in event notifier

We must serialize the release notifier and the config netlink function. A concurrent thread can issue close() which can call the release function while unrelated socket processes UNBIND request for same portid:

Oops: general protection fault, [..] RIP: 0010:instancedestroy+0x60/0x210 [nfnetlinkqueue] Call Trace: nfqnlrecvconfig+0x9b0/0xdc0 [nfnetlinkqueue] nfnetlinkrcvmsg+0x7c2/0xeb0 ? pfxnfnetlinkrcvmsg+0x10/0x10

After this, parallel UNBIND and URELEASE events are impossible.

This change isn't nice, but its the shortest fix given instances are not refcounted and the nfnetlink config callback drops the rcu read lock early due to need for sleeping allocations.