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Needs to happen before fopen($hosts, "w") as it is going to truncate the file
and that breaks the tracking of hosts size in dhcpleases.

Ticket:	#9383

Revise return_gateways_array() to include the tier name in hte returned array. This avoids the need to call the function for every gateway in the array and makes life easier for system_gateways.php, which no longer needs to call multiple functions to get the display information.