This diff replaces engine/netx code with netxlite code in
the engine/session.go file. To this end, we needed to move
some code from engine/netx to netxlite. While there, we
did review and improve the unit tests.
A notable change in this diff is (or seems to be) that in
engine/session.go we're not filtering for bogons anymore so
that, in principle, we could believe a resolver returning
to us bogon IP addresses for OONI services. However, I did
not bother with changing bogons filtering because the
sessionresolver package is already filtering for bogons,
so it is actually okay to avoid doing that again the
session.go code. See:
https://github.com/ooni/probe-cli/blob/v3.15.0-alpha.1/internal/engine/internal/sessionresolver/resolvermaker.go#L88
There are two reference issues for this cleanup:
1. https://github.com/ooni/probe/issues/2115
2. https://github.com/ooni/probe/issues/2121
