apps/netutils/telnetd: Add protection when CONFIG_SCHED_HAVE_PARENT is...

apps/netutils/telnetd:  Add protection when CONFIG_SCHED_HAVE_PARENT is enabled:  Call sigaction with SA_NOCLDWAIT so that exit status is not retained (no zombies) and block receipt of SIGCHLD so that accept is not awakened by a signal.  Iff accept() is awakened by a signal, do not do anything crazy like exit.  Most from Rony Xln