af_unix: read UNIX_DIAG_VFS data under unix_state_lock

In the Linux kernel, the following vulnerability has been resolved: af_unix: read UNIX_DIAG_VFS data under unix_state_lock Exact UNIX diag lookups hold a reference to the socket, but not to u->path. Meanwhile, unix_release_sock() clears u->path under unix_state_lock() and drops the path reference after unlocking. Read the inode and device numbers for UNIX_DIAG_VFS while holding unix_state_lock(), then emit the netlink attribute after dropping the lock. This keeps the VFS data stable while the reply is being built.