syscall: fix openbsd sysctl hostname/domainname workaround

Fixes #2509.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5451055

src/pkg/syscall/syscall_bsd.go

@@ -563,7 +563,7 @@ func Sysctl(name string) (value string, err error) {
 		// Work around a bug that was fixed after OpenBSD 5.0.
 		// The length for kern.hostname and kern.domainname is always
 		// returned as 0 when a nil value is passed for oldp.
-		if OS == "openbsd" && (value == "kern.hostname" || value == "kern.domainname") {
+		if OS == "openbsd" && (name == "kern.hostname" || name == "kern.domainname") {
 			// MAXHOSTNAMELEN
 			n = 256
 		} else {