Add config options for max pending connections, for both outgoing and incoming

[Voxelot]

          ... this defines the number of max established "incoming" connections, I arbitrarily set it to be 50% of total connections allowed, so 50:50 between incoming and outgoing connections. But we can have this configurable in p2p config if we want, plus maybe we should add config options for max pending connections, for both outgoing and incoming.

Originally posted by @leviathanbeak in #876 (comment)