SubscriptionController: fix subscription updating

We need to only repost messages on events we have handled, not
prematurely posting them for every single eveng incoming.

Furthermore, getMaxActive should return the MAX, not the current max.

The previous fixed dual sim insertion and removal ONLY if there were two
sims, but switching from two to one would break.

Ticket: CYNGNOS-2185, CYNGNOS-2570

Change-Id: I5b829662b466f609cd22adfa7d3b754757258463
Signed-off-by: Roman Birg <roman@cyngn.com>