[Foundation] Ensure that we allow celullar data by default until the user says otherwise. #6762 (#6916)

* [Foundation] Ensure that we allow celullar data by default until the user says otherwise. #6762

The default value in the NSUrlSession is to allow cellular data. This
small change closes the issue, since users will not have an unexpected
result.

Later we need to provide a proper fix to allow the property to be
exposed AND used the value of the session.

Fixes: https://github.com/xamarin/xamarin-macios/issues/6762

src/Foundation/NSUrlSessionHandler.cs

@@ -158,7 +158,7 @@ namespace Foundation {
 			// therefore, we do not have to listen to the notifications.
 			isBackgroundSession = !string.IsNullOrEmpty (configuration.Identifier);
 #endif
-
+			allowsCellularAccess = configuration.AllowsCellularAccess;
 			AllowAutoRedirect = true;
 
 			// we cannot do a bitmask but we can set the minimum based on ServicePointManager.SecurityProtocol minimum
@@ -280,7 +280,7 @@ namespace Foundation {
 			}
 		}
 
-		bool allowsCellularAccess;
+		bool allowsCellularAccess = true;
 
 		public bool AllowsCellularAccess {
 			get {

tests/monotouch-test/System.Net.Http/MessageHandlers.cs

@@ -15,6 +15,7 @@ using System.IO;
 using NUnit.Framework;
 using System.Net.Http.Headers;
 using System.Text;
+using Foundation;
 #if MONOMAC
 using Foundation;
 #endif
@@ -272,5 +273,20 @@ namespace MonoTests.System.Net.Http
 				}
 			}
 		}
+
+		[Test]
+		public void AssertDefaultValuesNSUrlSessionHandler ()
+		{
+			using (var handler = new NSUrlSessionHandler ()) {
+				Assert.True (handler.AllowAutoRedirect, "Default redirects value");
+				Assert.True (handler.AllowsCellularAccess, "Default cellular data value.");
+			}
+			using (var config = NSUrlSessionConfiguration.DefaultSessionConfiguration) {
+				config.AllowsCellularAccess = false;
+				using (var handler = new NSUrlSessionHandler (config)) {
+					Assert.False (handler.AllowsCellularAccess, "Configuration cellular data value.");
+				}
+			}
+		}
 	}
 }