ipv4: simplify init function for freebsd

Change-Id: I0713af6a5005ad4b917a2496a8ed023e92ab4174
Reviewed-on: https://go-review.googlesource.com/11292
Reviewed-by: Ian Lance Taylor <iant@golang.org>

ipv4/sys_freebsd.go

@@ -47,8 +47,8 @@ func init() {
 	}
 	if runtime.GOOS == "freebsd" && runtime.GOARCH == "386" {
 		archs, _ := syscall.Sysctl("kern.supported_archs")
-		for _, s := range strings.Split(archs, " ") {
-			if strings.TrimSpace(s) == "amd64" {
+		for _, s := range strings.Fields(archs) {
+			if s == "amd64" {
 				freebsd32o64 = true
 				break
 			}