tipc: fix infinite loop in __tipc_nl_compat_dumpit

In the Linux kernel, the following vulnerability has been resolved: tipc: fix infinite loop in __tipc_nl_compat_dumpit cmd->dumpit callback can return a negative errno, causing an infinite loop due to the while(len) condition. As the loop never terminates, genl_mutex is never released, and other tasks waiting on it starve in D state. Check dumpit's return value, propagate it and jump to err_out on error.