Fix flaky UdpEncapsulationSocket test

This commit reduces the flakiness of the
testOpenAndCloseUdpEncapsulationSocket by retrying up to three times.
Unfortunately, testing port-selected socket creation is racy against
other applications. This helps to handle the same race condition as done
in IpSecService#bindToRandomPort

Bug: 128024100
Test: 200x runs of testOpenAndCloseUdpEncapsulationSocket
Change-Id: I7e036ce821019dbac6c50899bd0894e89d2fe82a
Merged-In: Idf040a67e53d9b9ec6e6c647ce24f8ada501d355
Merged-In: Iad9aea4b42cd8b31a5a2659bb9cb54dd1c64e8b7
(cherry picked from commit 13fda9e39bdaf5f0503c8db68b4560a2c0034c49)
diff --git a/services/core/java/com/android/server/IpSecService.java b/services/core/java/com/android/server/IpSecService.java
index 126bf65..2cfcecc 100644
--- a/services/core/java/com/android/server/IpSecService.java
+++ b/services/core/java/com/android/server/IpSecService.java
@@ -96,9 +96,10 @@
             new int[] {OsConstants.AF_INET, OsConstants.AF_INET6};
 
     private static final int NETD_FETCH_TIMEOUT_MS = 5000; // ms
-    private static final int MAX_PORT_BIND_ATTEMPTS = 10;
     private static final InetAddress INADDR_ANY;
 
+    @VisibleForTesting static final int MAX_PORT_BIND_ATTEMPTS = 10;
+
     static {
         try {
             INADDR_ANY = InetAddress.getByAddress(new byte[] {0, 0, 0, 0});