This provides an easy iterator type for iterating netns in
the default pinned directory.
This being a simple function that returns the iterator will
allow for easy test mocking in subsequent commands where we
want to create real network-namespaces, but don't necessarily
need to pin them to the filesystem.

Errors are aggregated in a buffered channel so they can be
accessed during iteration.

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

This abstracts concern related to iterating netns and
uses the new netns.All() function to replace the current
default functionality parity.

This will allow for providing an iterator that doesn't
rely on pinned netns (i.e. just ones we create at runtime
for the test process) which will make it easier to test.

As well, switch global use of *option.Config to a field
now provided via hive. This will avoiding global options
mutation for tests.

Finally, we now return errors from the terminate function,
although we do not handle it as errors are already logged.
The purpose is to return errors while testing in following
commits.

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

This provides integration testing to test service manager
TerminateUDPConnectionsToBackend functionality together
with sockets.Destroy implementation.

Note: This is committed prior to further changes to
pkg/datapath/sockets code to validate that tests succeed
before and after the change.

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

Instead of having a custom function for iterating UDP connections
rename and change this function to: iterateNetlinkSockets.

iterateNetlinkSockets will be able iterate any type of socket via
the netlink api.

In subsequent commits, this will be used to make the datapath/sockets
library a general purpose sockets library that allows for separately
iterating and destroying sockets via netlink.

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

This is used to validate that subsequent changes do
not introduce regressions to functionality relying on
sockets.Destroy (i.e. svc-LB UDP sock destroy).

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

Note: Up to this change was benchmarks to validate no memory
usage regressions are introduced following previous optimizations
in previous commits:

-------------
New:
-------------

goos: linux
goarch: arm64
pkg: github.com/cilium/cilium/pkg/datapath/sockets
BenchmarkSocketReqSerialize-8           69173708               174.3 ns/op           128 B/op          2 allocs/op
BenchmarkSocketDeserialize-8            159207418               75.43 ns/op           64 B/op          4 allocs/op
PASS
ok      github.com/cilium/cilium/pkg/datapath/sockets   31.865s

-------------
Old:
-------------

goos: linux
goarch: arm64
pkg: github.com/cilium/cilium/pkg/datapath/sockets
BenchmarkSocketReqSerialize-8           69530899               172.2 ns/op           128 B/op          2 allocs/op
BenchmarkSocketDeserialize-8            163702172               73.25 ns/op           64 B/op          4 allocs/op
PASS
ok      github.com/cilium/cilium/pkg/datapath/sockets   31.551s

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

The only consumer of this code is (currently) service
manager so we should reflect that in reviews.

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>