CVE-2026-53181: vsock/vmci: fix sk_ack_backlog leak on failed handshake

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

vsock/vmci: fix skackbacklog leak on failed handshake

When vmcitransportrecvconnectingserver() returns an error, vmcitransportrecvlisten() calls vsockremovepending() but never calls skacceptqremoved(). This leaves skackbacklog incremented permanently.

Repeated handshake failures (malformed packets, queue pair alloc failure, event subscribe failure) cause skackbacklog to climb toward skmaxackbacklog. Once it reaches the limit the listener permanently refuses all new connections with -ECONNREFUSED, a silent denial of service requiring a process restart to recover.

The two existing skacceptqremoved() calls in afvsock.c do not cover this path: line 764 checks vsockispending() which returns false after vsockremovepending(), and line 1889 is only reached on successful accept().

Fix by balancing skacceptqadded() with skacceptqremoved() on the error path.