sysctl: make privileged tests build again
sysctl: make privileged tests build again

Fix the follow test build errors:

```
 # github.com/cilium/cilium/pkg/sysctl [github.com/cilium/cilium/pkg/sysctl.test]
 pkg/sysctl/sysctl_linux_privileged_test.go:43:4: cannot use "1" (type string) as type []byte in field value
 pkg/sysctl/sysctl_linux_privileged_test.go:48:4: cannot use "1" (type string) as type []byte in field value
 pkg/sysctl/sysctl_linux_privileged_test.go:53:4: cannot use "1" (type string) as type []byte in field value
 pkg/sysctl/sysctl_linux_privileged_test.go:58:4: cannot use "1" (type string) as type []byte in field value
 pkg/sysctl/sysctl_linux_privileged_test.go:64:33: cannot use tc.value (type []byte) as type string in argument to writeSysctl
```

Signed-off-by: Tobias Klauser <9249c549618448e4c699e8032ba6c7f0d7fd4b7f@distanz.ch>

michi-covalent/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,cilium-team/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,cilium-team/cilium,tgraf/cilium,michi-covalent/cilium