Do not release prefix too early

The hotspotPrefix was previously released on line 192, so when a new
prefix was allocated on line 206, it was allowed to "conflict" with the
now-released hotspotPrefix.

This change moves the call to releaseDownstream() to the end, so the
test can properly check for conflicts.

Test: TH
Bug: 375858174
Change-Id: Iac786237340fc14098701d86fa80946a7fb8e0b6
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/PrivateAddressCoordinatorTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/PrivateAddressCoordinatorTest.java
index 1608e1a..c329142 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/PrivateAddressCoordinatorTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/PrivateAddressCoordinatorTest.java
@@ -189,7 +189,6 @@
         final LinkAddress hotspotAddress = requestDownstreamAddress(mHotspotIpServer);
         final IpPrefix hotspotPrefix = asIpPrefix(hotspotAddress);
         assertNotEquals(asIpPrefix(mBluetoothAddress), hotspotPrefix);
-        releaseDownstream(mHotspotIpServer);
 
         // - Test previous enabled hotspot prefix(cached prefix) is reserved.
         when(mPrivateAddressCoordinator.getRandomInt()).thenReturn(
@@ -208,6 +207,7 @@
         assertNotEquals(asIpPrefix(mLegacyWifiP2pAddress), etherPrefix);
         assertNotEquals(asIpPrefix(mBluetoothAddress), etherPrefix);
         assertNotEquals(hotspotPrefix, etherPrefix);
+        releaseDownstream(mHotspotIpServer);
         releaseDownstream(mEthernetIpServer);
     }