Since being online is a privileged operation, it’s better to fail-safe
and make the `Context` offline by default unless explicitly initialised
(e.g. with `context_from_cmdline()` or an explicit initialisation of
`.offline = false`).
There are a few instances where `.offline = true` is set explicitly.
I’ve left those in place, even though they’re now redundant, as
documentation.
Signed-off-by: Philip Withnall <pwithnall@gnome.org>
(cherry picked from commit 97183383af03279c43d9c270af5832d36d527d01)