Updated GetSession to use lock

src/dotnet/src/Mil.Navy.Nrl.Norm/NormSession.cs

@@ -1,5 +1,4 @@
-using System.Runtime.CompilerServices;
-using System.Text;
+using System.Text;
 
 namespace Mil.Navy.Nrl.Norm
 {
@@ -75,11 +74,13 @@ namespace Mil.Navy.Nrl.Norm
         /// </summary>
         /// <param name="handle">Specifies the session to return.</param>
         /// <returns>Returns a NormSession.</returns>
-        [MethodImpl(MethodImplOptions.Synchronized)]
         internal static NormSession GetSession(long handle)
+        {
+            lock (_normSessions)
             {
                 return _normSessions[handle];
             }
+        }
 
         /// <summary>
         /// This function immediately terminates the application's participation in the NormSession and frees any resources used by that session.