fix(android): avoid API 26 network callback overload on Android 7

Author: atavism

android/app/src/main/kotlin/org/getlantern/lantern/service/DefaultNetworkListener.kt

@@ -169,9 +169,13 @@ object DefaultNetworkListener {
                     mainHandler
                 )
             }
-            in 24..30 -> {
+            in 26..30 -> {
                 LanternApp.connectivity.registerDefaultNetworkCallback(Callback, mainHandler)
             }
+            // Handler overload was added in API 26; API 24-25 only have the one-arg version.
+            in 24..25 -> {
+                LanternApp.connectivity.registerDefaultNetworkCallback(Callback)
+            }
             else -> try {
                 fallback = false
                 LanternApp.connectivity.registerDefaultNetworkCallback(Callback)
@@ -187,4 +191,4 @@ object DefaultNetworkListener {
             LanternApp.connectivity.unregisterNetworkCallback(Callback)
         }
     }
-}
+}