Fix the MTU logic

pkg/sml/transport.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/hashicorp/memberlist"
+	"github.com/sirupsen/logrus"
 	"golang.org/x/net/ipv6"
 )
 
@@ -38,18 +39,24 @@ func NewTransport(config *memberlist.NetTransportConfig) (*instrumentedTransport
 func (t *instrumentedTransport) DialAddressTimeout(a memberlist.Address, timeout time.Duration) (net.Conn, error) {
 	addr := a.Addr
 
+	logrus.Debugf("memberlist dialing %s", addr)
 	dialer := net.Dialer{Timeout: timeout}
 	conn, err := dialer.Dial("tcp", addr)
 	if err == nil {
 		wrapped := ipv6.NewConn(conn)
 		mtu, err := wrapped.PathMTU()
-		if err != nil {
+		if err == nil {
+			logrus.Debugf("node %s has MTU %d", addr, mtu)
 			prev, _ := t.pmtu[addr]
 			t.pmtu[addr] = mtu
 			if prev != mtu {
 				t.updateMinMTU()
 			}
+		} else {
+			logrus.Debug(err)
 		}
+	} else {
+		logrus.Debug(err)
 	}
 	return conn, err
 }