Instead of every module having to come up with a set of test methods for
the event bus, this handful of test helpers hides a lot of the needed
setup for the testing of the event bus.
The tests in portmapper is also ported over to the new helpers.
Updates #15160
Signed-off-by: Claus Lensbøl <claus@tailscale.com>
Fragmented datagrams would be processed instead of being dumped right
away. In reality, thse datagrams would be dropped anyway later so there
should functionally not be any change. Additionally, the feature is off
by default.
Closes#16203
Signed-off-by: Claus Lensbøl <claus@tailscale.com>