network: Use kernel/user space header files

Add and use <machine/rtems-bsd-kernel-space.h> and
<machine/rtems-bsd-user-space.h> similar to the libbsd to avoid command
line defines and defines scattered throught the code base.

Simplify cpukit/libnetworking/Makefile.am.

Update #3375.

bsps/lm32/shared/net/network.c

@@ -10,7 +10,7 @@
  *  Copyright (C) 2011 Sebastien Bourdeauducq
  */
 
-#define __INSIDE_RTEMS_BSD_TCPIP_STACK__
+#include <machine/rtems-bsd-kernel-space.h>
 #define RTEMS_STATUS_CHECKS_USE_PRINTK
 
 #include <bsp.h>

bsps/lm32/shared/net/tsmac.c

@@ -12,8 +12,7 @@
  *  Micro-Research Finland Oy
  */
 
-#define __INSIDE_RTEMS_BSD_TCPIP_STACK__
-#define _KERNEL
+#include <machine/rtems-bsd-kernel-space.h>
 
 #include <rtems.h>
 #include <bsp.h>