[gomobile-lib] better control over the max number of connected peers

[aeddi]

For the moment, the limits that we set in the config concerning the number of peers (high/low watermarks, grace period) does not seem to regulate correctly the maximum number of connected peers (probably due to a misuse / misunderstanding on our part).

We need to find a way to precisely control the maximum number of peers a device is connected to because:

• On iOS and Android, the number of connected peers is strongly related to the resource consumption
• On iOS a problem occurs very quickly: the OS throws "too many open files" errors when it reaches about 200 connected peers (this limit is not configurable on iOS)

I will do precise tests with different high/low watermarks and grace period settings and post reports on this issue so that we have a better view of the problem before thinking about solutions.