import gopacket from github instaead of google code

The latter redirects to the former, which breaks `go get`.

Closes #1071.

prog/weaver/main.go

@@ -11,8 +11,8 @@ import (
 	"runtime"
 	"strings"
 
-	"code.google.com/p/gopacket/layers"
 	"github.com/davecheney/profile"
+	"github.com/google/gopacket/layers"
 	"github.com/gorilla/mux"
 	. "github.com/weaveworks/weave/common"
 	"github.com/weaveworks/weave/common/docker"

router/ethernet_decoder.go

@@ -2,8 +2,8 @@ package router
 
 import (
 	"bytes"
-	"code.google.com/p/gopacket"
-	"code.google.com/p/gopacket/layers"
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
 	"log"
 	"net"
 )

router/forwarder.go

@@ -1,8 +1,8 @@
 package router
 
 import (
-	"code.google.com/p/gopacket"
-	"code.google.com/p/gopacket/layers"
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
 	"syscall"
 	"time"
 )

router/pcap.go

@@ -1,8 +1,8 @@
 package router
 
 import (
-	"code.google.com/p/gopacket/pcap"
 	"fmt"
+	"github.com/google/gopacket/pcap"
 )
 
 type PcapIO struct {

router/router.go

@@ -11,7 +11,7 @@ import (
 	"syscall"
 	"time"
 
-	"code.google.com/p/gopacket/layers"
+	"github.com/google/gopacket/layers"
 	. "github.com/weaveworks/weave/common"
 )
 

router/udp_sender.go

@@ -1,8 +1,8 @@
 package router
 
 import (
-	"code.google.com/p/gopacket"
-	"code.google.com/p/gopacket/layers"
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
 	"log"
 	"net"
 	"syscall"