Allow inbound connections of known static peers without outbound connections

[shufps]

There are cases where e.g. exchanges want to establish outbound connections to the IF without allowing inbound connections from external nodes.

A node can be promoted to "known relation" by adding the multiaddress of the external node to the peering.json, but after adding, Hornet will continuosly try to establish a connection to the external node even if it is not wanted (or not possible because it is not reachable due to firewall restrictions).

It would be great, if outbound connections could be deactivated (e.g. by putting a ! into the DNS name of the multiaddress) - or in some other way.