Use the non-server default connection limit for unityaot (case 1156607)

The default value for `DefaultConnectionLimit`, which is set based on
the `DefaultPersistentConnectionLimit` value should be 2 for all
non-ASP.NET applications.

So for the unityaot profile, used with IL2CPP, use the value of 2.

Author: Josh Peterson

mcs/class/System/System.Net/ServicePointManager.cs

@@ -132,7 +132,7 @@ public override bool Equals (object obj) {
 		// Fields
 
 		public const int DefaultNonPersistentConnectionLimit = 4;
-#if MOBILE
+#if MOBILE && !UNITY_AOT
 		public const int DefaultPersistentConnectionLimit = 10;
 #else
 		public const int DefaultPersistentConnectionLimit = 2;