server: in peerBootstrapper check for enough conns before attempting backoff
server: in peerBootstrapper check for enough conns before attempting backoff

In this commit we modify the main loop within the peerBootstrapper
slightly to check for a sufficient amount of connections, _before_
checking to see if we need to back off the main loop. With this, we
avoid unnecessarily backing off unless an actual error occurs.

LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd