Add peer no-preference selection strategy

[ShanniLi]

r @jcorbin @kriskowal @Raynos

Tested with Ringpop and observed the 2x connection issue gone.

[anson627]

so xlate egress should specify PreferOutgoing, since it only make outbound calls?

[kriskowal]

We’ll also need preferIncoming for service channels speaking to Hyperbahn, so they favor connections from their affine nodes. The eventual API should be preferConnectionDirection: 'incoming' | 'outgoing' | null to avoid weird cases like preferIncoming: true, preferOutgoing: true. Other than that, this looks solid.

[ShanniLi]

@anson627 xlate egress is a hyperbahn service, right? If so, it should prefer incoming.

[Raynos]

We should add some tests.

test('prefer outgoing creates new conn even if incoming');
test('prefer any re-uses incoming conn and does not open outgoing conn');

[Raynos]

The main aim of tests is:

• to assert that for prefer outgoing there are two connection objects between two tchannels.
• to assert that for prefer any there is only one connection between two tchannels.

[Raynos]

lgtm