Constructs a new instance of this class. Once started, the thread checks network availability at a specified
frequency and stores the result in an atomic variable specified to the constructor. The thread terminates when
it's interrupted or when a specified boolean atomic variable has the value false.
showNetStatus - a reference to an atomic variable indicating whether the thread should continue running.
This variable is tested prior to each network check. The thread terminates when it becomes
isNetAvailable - a reference to an atomic variable in which to write the status of the network check.
interval - the interval at which to perform the network check, or null if the default interval of one
second is to be used.