net/netns: implement UseSocketMark for Android.
Build fails on Android:
`../../../../go/pkg/mod/tailscale.com@v1.1.1-0.20220916223019-65c24b6334e9/wgengine/magicsock/magicsock_linux.go:133:12: undefined: netns.UseSocketMark`
androidProtectFunc func(fd int) error
)
+// UseSocketMark reports whether SO_MARK is in use. Android does not use SO_MARK.
+func UseSocketMark() bool {
+ return false
+}
+
// SetAndroidProtectFunc register a func that Android provides that JNI calls into
// https://developer.android.com/reference/android/net/VpnService#protect(int)
// which is documented as:
