Refactor make{Tether4Key, Tether4Value ConntrackEvent} helper

Used for reducing the increasing amount of helper in the
follow-up commits.

Tether4Key, Tether4Value ConntrackEvent need many arguments to build
a testing instance. Any new argument combination may require a new
helper. It is hard to compare the difference while reading the code.

Test: atest BpfCoordinatorTest
Change-Id: I5af6ce9609b97d124227750cd1c5337796982c58
1 file changed