Return a port from bindToPort() in IpSecService

When binding to a random port, the port number was not being
returned, so the user is incorrectly receiving a port of zero.
Return the port number that was ultimately bound.

Bug: 67662580
Test: Ran CTS test on aosp_angler-eng
Change-Id: I22f4e5cdc83d43dc453788889990feb34e451bd3

services/core/java/com/android/server/IpSecService.java

@@ -754,7 +754,7 @@ public class IpSecService extends IIpSecService.Stub {
      * and re-binding, during which the system could *technically* hand that port out to someone
      * else.
      */
-    private void bindToRandomPort(FileDescriptor sockFd) throws IOException {
+    private int bindToRandomPort(FileDescriptor sockFd) throws IOException {
         for (int i = MAX_PORT_BIND_ATTEMPTS; i > 0; i--) {
             try {
                 FileDescriptor probeSocket = Os.socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
@@ -763,7 +763,7 @@ public class IpSecService extends IIpSecService.Stub {
                 Os.close(probeSocket);
                 Log.v(TAG, "Binding to port " + port);
                 Os.bind(sockFd, INADDR_ANY, port);
-                return;
+                return port;
             } catch (ErrnoException e) {
                 // Someone miraculously claimed the port just after we closed probeSocket.
                 if (e.errno == OsConstants.EADDRINUSE) {
@@ -803,7 +803,7 @@ public class IpSecService extends IIpSecService.Stub {
                 Log.v(TAG, "Binding to port " + port);
                 Os.bind(sockFd, INADDR_ANY, port);
             } else {
-                bindToRandomPort(sockFd);
+                port = bindToRandomPort(sockFd);
             }
             // This code is common to both the unspecified and specified port cases
             Os.setsockoptInt(