[posix] fix strncpy warning about null terminated string length (#6698)
[posix] fix strncpy warning about null terminated string length (#6698)


jwhui/openthread,srickardti/openthread,jwhui/openthread,abtink/openthread,srickardti/openthread,srickardti/openthread,jwhui/openthread,openthread/openthread,jwhui/openthread,openthread/openthread,openthread/openthread,openthread/openthread,srickardti/openthread,abtink/openthread,abtink/openthread,abtink/openthread