include: Try harder to redefine u_long, and avoid using it in headers as far as possible.
diff --git a/include/mstcpip.h b/include/mstcpip.h
index 25dcfe1..55fa542 100644
--- a/include/mstcpip.h
+++ b/include/mstcpip.h
@@ -18,9 +18,9 @@
 
 struct tcp_keepalive
 {
-    u_long onoff;
-    u_long keepalivetime;
-    u_long keepaliveinterval;
+    ULONG onoff;
+    ULONG keepalivetime;
+    ULONG keepaliveinterval;
 };
 
 #ifndef USE_WS_PREFIX