Implement incoming connections limit

[diego-G]

Expected behavior

When an incoming peer connection arises, the peer pool should check if the current incoming connections are below the maximum of incoming connections allowed (maxInConnections). Otherwise, an eviction method must be triggered to randomly remove an ongoing connection and therefore allow the fresh one.

The parameter maxInConnections must be configurable, discouraging the users to modify it in any non-experimental scenario. The proposed default value is 100.

Actual behavior

The node allows as much connections as the hardware supports.

Steps to reproduce

Which version(s) does this affect? (Environment, OS, etc...)

2.0.0+