network: Clear connectivity queue after portal login
When full connectivity (or rather, non-portal connectivity) is achieved,
we can clear all active portal helpers.
Normally, the portal helper will signal that it is done, but it is
implemented in a racy manner. So here let's do a comprehensive big
hammer solution to guarantee the portal helper definitely gets
eventually closed even if we miss the race window in the portal helper.
(The race is: the portal helper checks connectivity status either
immediately or within a certain amount of time after a navigation policy
decision. This could theoretically be too soon, and if missed, it won't
be rescheduled.)