gbn: increase defaultHandshakeTimeout to 1 second

Currently, the queue handshake timeout is cannot be set through options,
so it is always set to the defaultHandshakeTimeout. The queue handshake
timeout is used when determining if the queue should be resent or not,
and defines minimum time we need to wait before resending the queue
again. The value prior to this commit was 100ms, which is too low to
make an impact, as it's unlikely that we'll try to resend the queue
within 100ms of the last time we sent it.

gbn/gbn_conn.go

@@ -20,7 +20,7 @@ var (
 
 const (
 	DefaultN                = 20
-	defaultHandshakeTimeout = 100 * time.Millisecond
+	defaultHandshakeTimeout = 1000 * time.Millisecond
 	defaultResendTimeout    = 2000 * time.Millisecond
 	finSendTimeout          = 1000 * time.Millisecond
 	defaultResendMultiplier = 5

gbn/queue.go

@@ -39,7 +39,10 @@ type queue struct {
 	// topMtx is used to guard sequenceTop.
 	topMtx sync.RWMutex
 
-	lastResend       time.Time
+	lastResend time.Time
+
+	// handshakeTimeout defines minimum time we need to wait before
+	// resending the queue again, since the last time we resent it.
 	handshakeTimeout time.Duration
 }