fix link statistics pointer alignment

gc's `-d checkptr` option reported the following problem:
```
--- FAIL: TestAddrAdd (0.00s)
panic: runtime error: unsafe pointer conversion [recovered]
	panic: runtime error: unsafe pointer conversion

goroutine 19 [running]:
testing.tRunner.func1(0xc00011a240)
	go/src/testing/testing.go:916 +0xaeb
panic(0x7f5c80, 0xc00013a100)
	go/src/runtime/panic.go:973 +0x396
github.com/vishvananda/netlink.LinkDeserialize(0x0, 0xc000174010, 0x514, 0x514, 0x1, 0x1, 0x0, 0x0)
	netlink/link_linux.go:1674 +0x33c5
github.com/vishvananda/netlink.execGetLink(0xc0001540a0, 0xc00013a0a0, 0x2, 0x2, 0x3)
	netlink/link_linux.go:1495 +0x205
github.com/vishvananda/netlink.(*Handle).LinkByName(0xa95e70, 0x81c4c9, 0x2, 0x4, 0x4, 0xc, 0x1)
	netlink/link_linux.go:1415 +0x578
github.com/vishvananda/netlink.LinkByName(...)
	netlink/link_linux.go:1395
github.com/vishvananda/netlink.DoTestAddr(0xc00011a240, 0x82d878)
	netlink/addr_test.go:62 +0xfbc
github.com/vishvananda/netlink.TestAddrAdd(0xc00011a240)
	netlink/addr_test.go:15 +0x45
testing.tRunner(0xc00011a240, 0x82d898)
	go/src/testing/testing.go:954 +0x1ec
created by testing.(*T).Run
	go/src/testing/testing.go:1005 +0x661
FAIL	github.com/vishvananda/netlink	0.006s
FAIL
```

Make sure the link structures are properly aligned.

link_linux.go

@@ -1515,8 +1515,8 @@ func LinkDeserialize(hdr *unix.NlMsghdr, m []byte) (Link, error) {
 	}
 	var (
 		link      Link
-		stats32   []byte
-		stats64   []byte
+		stats32   *LinkStatistics32
+		stats64   *LinkStatistics64
 		linkType  string
 		linkSlave LinkSlave
 		slaveType string
@@ -1669,9 +1669,15 @@ func LinkDeserialize(hdr *unix.NlMsghdr, m []byte) (Link, error) {
 		case unix.IFLA_IFALIAS:
 			base.Alias = string(attr.Value[:len(attr.Value)-1])
 		case unix.IFLA_STATS:
-			stats32 = attr.Value[:]
+			stats32 = new(LinkStatistics32)
+			if err := binary.Read(bytes.NewBuffer(attr.Value[:]), nl.NativeEndian(), stats32); err != nil {
+				return nil, err
+			}
 		case unix.IFLA_STATS64:
-			stats64 = attr.Value[:]
+			stats64 = new(LinkStatistics64)
+			if err := binary.Read(bytes.NewBuffer(attr.Value[:]), nl.NativeEndian(), stats64); err != nil {
+				return nil, err
+			}
 		case unix.IFLA_XDP:
 			xdp, err := parseLinkXdp(attr.Value[:])
 			if err != nil {
@@ -1716,9 +1722,9 @@ func LinkDeserialize(hdr *unix.NlMsghdr, m []byte) (Link, error) {
 	}
 
 	if stats64 != nil {
-		base.Statistics = parseLinkStats64(stats64)
+		base.Statistics = (*LinkStatistics)(stats64)
 	} else if stats32 != nil {
-		base.Statistics = parseLinkStats32(stats32)
+		base.Statistics = (*LinkStatistics)(stats32.to64())
 	}
 
 	// Links that don't have IFLA_INFO_KIND are hardware devices
@@ -2483,14 +2489,6 @@ func parseGretunData(link Link, data []syscall.NetlinkRouteAttr) {
 	}
 }
 
-func parseLinkStats32(data []byte) *LinkStatistics {
-	return (*LinkStatistics)((*LinkStatistics32)(unsafe.Pointer(&data[0:SizeofLinkStats32][0])).to64())
-}
-
-func parseLinkStats64(data []byte) *LinkStatistics {
-	return (*LinkStatistics)((*LinkStatistics64)(unsafe.Pointer(&data[0:SizeofLinkStats64][0])))
-}
-
 func addXdpAttrs(xdp *LinkXdp, req *nl.NetlinkRequest) {
 	attrs := nl.NewRtAttr(unix.IFLA_XDP|unix.NLA_F_NESTED, nil)
 	b := make([]byte, 4)