NetworkCapabilities: Added support for TRANSPORT_LOWPAN

This change simply adds a new constant, `TRANSPORT_LOWPAN`, for
identifying low-power wireless networks like Thread.

Bug: b/33073713
Merged-In: Ie4aa77496f8ff466fa1a5fbc556e9c029457a689

(cherry pick from commit 103292d0b7)

Change-Id: I21f9b41b8b31c63ceeb1bc9c965f6da2614c356a

Test: runtest frameworks-net (not in original commit message)

core/java/android/net/NetworkCapabilities.java

@@ -418,10 +418,16 @@ public final class NetworkCapabilities implements Parcelable {
      */
     public static final int TRANSPORT_WIFI_AWARE = 5;
 
+    /**
+     * Indicates this network uses a LoWPAN transport.
+     * @hide
+     */
+    public static final int TRANSPORT_LOWPAN = 6;
+
     /** @hide */
     public static final int MIN_TRANSPORT = TRANSPORT_CELLULAR;
     /** @hide */
-    public static final int MAX_TRANSPORT = TRANSPORT_WIFI_AWARE;
+    public static final int MAX_TRANSPORT = TRANSPORT_LOWPAN;
 
     private static final String[] TRANSPORT_NAMES = {
         "CELLULAR",
@@ -429,7 +435,8 @@ public final class NetworkCapabilities implements Parcelable {
         "BLUETOOTH",
         "ETHERNET",
         "VPN",
-        "WIFI_AWARE"
+        "WIFI_AWARE",
+        "LOWPAN"
     };
 
     /**