htlcswitch+peer: set and read aux custom records

This is the final step, we actually call the interface and either
provide or retrieve the custom features over the message. We also notify
the aux components when channel reestablish is received.

server.go

@@ -4431,6 +4431,7 @@ func (s *server) peerConnected(conn net.Conn, connReq *connmgr.ConnReq,
 		AuxChanCloser:          s.implCfg.AuxChanCloser,
 		AuxResolver:            s.implCfg.AuxContractResolver,
 		AuxTrafficShaper:       s.implCfg.TrafficShaper,
+		AuxChannelNegotiator:   s.implCfg.AuxChannelNegotiator,
 		ShouldFwdExpEndorsement: func() bool {
 			if s.cfg.ProtocolOptions.NoExperimentalEndorsement() {
 				return false