Target SDK 29 for more efficient netlink

mobile/build.gradle.kts

@@ -10,6 +10,7 @@ plugins {
 
 android {
     val javaVersion = JavaVersion.VERSION_1_8
+    val targetSdk = 29
     compileOptions {
         isCoreLibraryDesugaringEnabled = true
         sourceCompatibility = javaVersion
@@ -23,7 +24,7 @@ android {
     defaultConfig {
         applicationId = "be.mygod.vpnhotspot"
         minSdkVersion(21)
-        targetSdkVersion(30)
+        targetSdkVersion(targetSdk)
         resConfigs(listOf("it", "ru", "zh-rCN", "zh-rTW"))
         versionCode = 224
         versionName = "2.9.1"
@@ -32,6 +33,7 @@ android {
                 "room.incremental" to "true",
                 "room.schemaLocation" to "$projectDir/schemas"))
         buildConfigField("boolean", "DONATIONS", "true")
+        buildConfigField("int", "TARGET_SDK", targetSdk.toString())
     }
     buildFeatures {
         dataBinding = true

mobile/src/main/java/be/mygod/vpnhotspot/net/monitor/IpMonitor.kt

@@ -5,6 +5,7 @@ import android.system.ErrnoException
 import android.system.OsConstants
 import androidx.core.content.edit
 import be.mygod.vpnhotspot.App.Companion.app
+import be.mygod.vpnhotspot.BuildConfig
 import be.mygod.vpnhotspot.R
 import be.mygod.vpnhotspot.util.RootSession
 import be.mygod.vpnhotspot.widget.SmartSnackbar
@@ -24,7 +25,8 @@ abstract class IpMonitor : Runnable {
                 "Dump (was interrupted and may be inconsistent.|terminated)$)").toRegex()
         var currentMode: Mode
             get() {
-                val defaultMode = if (Build.VERSION.SDK_INT < 30) @Suppress("DEPRECATION") {
+                val isLegacy = Build.VERSION.SDK_INT < 30 || BuildConfig.TARGET_SDK < 30
+                val defaultMode = if (isLegacy) @Suppress("DEPRECATION") {
                     Mode.Poll
                 } else Mode.MonitorRoot
                 return Mode.valueOf(app.pref.getString(KEY, defaultMode.toString()) ?: "")