NOVA: delegate EC cap solely with recall right

Vancouver recalls the vCPU in the vCPU dispatcher code. Enable the right bit
in the mapped native cap so that Vancouver actually is able to perform this
operation.

base-nova/src/core/include/platform_thread.h

@@ -125,7 +125,10 @@ namespace Genode {
 
 			Native_capability native_cap()
 			{
-				return Native_capability(_sel_ec(), 0);
+				using namespace Nova;
+
+				return Native_capability(
+					_sel_ec(), Obj_crd::RIGHT_EC_RECALL);
 			}
 
 	};