crypto/tls: don't rely on map iteration order.

Previously we were using the map iteration order to set the order of
the cipher suites in the ClientHello.

R=bradfitz
CC=golang-dev
https://golang.org/cl/5440048

src/pkg/crypto/tls/common.go

@@ -315,9 +315,7 @@ var (
 
 func initDefaultCipherSuites() {
 	varDefaultCipherSuites = make([]uint16, len(cipherSuites))
-	i := 0
-	for id := range cipherSuites {
-		varDefaultCipherSuites[i] = id
-		i++
+	for i, suite := range cipherSuites {
+		varDefaultCipherSuites[i] = suite.id
 	}
 }