kernel: tipc: fix a null-ptr-deref in tipc_topsrv_accept

In the Linux kernel, the following vulnerability has been resolved: tipc: fix a null-ptr-deref in tipctopsrvaccept syzbot found a crash in tipctopsrvaccept: KASAN: null-ptr-deref in range 0x0000000000000008-0x000000000000000f Workqueue: tipcrcv tipctopsrvaccept RIP: 0010:kernelaccept+0x22d/0x350...