This signifies the networking tier used for configuring this
load balancer and can only take the following values: PREMIUM,
STANDARD. For regional ForwardingRule, the valid values are
PREMIUM and STANDARD. For GlobalForwardingRule, the valid value
is PREMIUM.
If this field is not specified, it is assumed to be PREMIUM. If
IPAddress is specified, this value must be equal to the
networkTier of the Address.