android: Prevent FD leak from HttpURLConnection

The default is apparently "Connection: keep-alive", which somehow keeps
the socket around, which leaks file descriptors with every connection
that fetches OCSP and/or CRLs.  Over time that could result in the number
of FDs reaching a limit e.g. imposed by FD_SET().

Closes strongswan/strongswan#1160

src/frontends/android/app/src/main/java/org/strongswan/android/logic/SimpleFetcher.java

@@ -58,6 +58,7 @@ public class SimpleFetcher
 				HttpURLConnection conn = (HttpURLConnection) url.openConnection();
 				conn.setConnectTimeout(10000);
 				conn.setReadTimeout(10000);
+				conn.setRequestProperty("Connection", "close");
 				try
 				{
 					if (contentType != null)