_updateInterest () {
    const prev = this._amInterested
    this._amInterested = !!this._selections.length

    this.wires.forEach(wire => this._updateWireInterest(wire))

    if (prev === this._amInterested) return
    if (this._amInterested) this.emit('interested')
    else this.emit('uninterested')
  }
Update interested status for all peers.