nixos/tests/networking: fix DHCP range
nixos/tests/networking: fix DHCP range

Exclude static 192.168.*.2 addresses from the dynamic address range to
prevent different interfaces from getting the same address.

Seems like configuring a fixed IPv4 address does not automatically
exclude it from the dynamic address range.

Should fix occasional failures of
nixos.tests.networking.scripted.macvlan and possibly other networking
tests relying on DHCP.

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