fwupd: do fwupd_client_connect before setting user agent

Since fwupd 1.8.11, setting user agent before doing anything else
causes an error, because the daemon version is not yet set and
the user agent setting function now errors out if that's the
case (previously it set part of the user agent string as NULL,
which was bad and apparently confused LVFS). gnome-software does
client_connect (well, it uses the async version) before setting
the user agent, so let's try that (moving it from happening just
*after* setting the user agent).

Signed-off-by: Adam Williamson <awilliam@redhat.com>