task #14314: include cleanups

Couple of more cleanups for task #14314 involving includes:
  1) if.h name should match if_api.c due to LwIP convention and history.
     Standard if.h include can be used with compatibility header in
     posix/net/if.h
  2) API header (if.h) should not be included in core code. This include
     has been eliminated by moving the definition of IF_NAMESIZE to
     netif.h as NETIF_NAMESIZE.  This is now the canonical definition
     and IF_NAMESIZE just maps to it to provide the standard type

src/include/lwip/if_api.h

@@ -40,8 +40,9 @@
 #define LWIP_HDR_IF_H
 
 #include "lwip/opt.h"
+#include "lwip/netif.h"
 
-#define IF_NAMESIZE 6 /* 2 chars, 3 nums, 1 \0 */
+#define IF_NAMESIZE NETIF_NAMESIZE
 
 char * lwip_if_indextoname(unsigned int ifindex, char *ifname);
 unsigned int lwip_if_nametoindex(const char *ifname);

src/include/lwip/netif.h

@@ -63,6 +63,12 @@ extern "C" {
 #define NETIF_MAX_HWADDR_LEN 6U
 #endif
 
+/** The size of a fully constructed netif name which the
+ * netif can be identified by in APIs. Composed of
+ * 2 chars, 3 (max) digits, and 1 \0
+ */
+#define NETIF_NAMESIZE 6
+
 /**
  * @defgroup netif_flags Flags
  * @ingroup netif

src/include/lwip/netifapi.h

@@ -40,7 +40,6 @@
 #include "lwip/netif.h"
 #include "lwip/dhcp.h"
 #include "lwip/autoip.h"
-#include "lwip/if.h"
 #include "lwip/priv/tcpip_priv.h"
 
 #ifdef __cplusplus
@@ -76,7 +75,7 @@ struct netifapi_msg {
     } common;
     struct {
 #if LWIP_MPU_COMPATIBLE
-      char name[IF_NAMESIZE];
+      char name[NETIF_NAMESIZE];
 #else /* LWIP_MPU_COMPATIBLE */
       char *name;
 #endif /* LWIP_MPU_COMPATIBLE */

src/include/posix/net/if.h

@@ -1,6 +1,6 @@
 /**
  * @file
- * This file is a posix wrapper for lwip/if.h.
+ * This file is a posix wrapper for lwip/if_api.h.
  */
 
 /*
@@ -30,4 +30,4 @@
  *
  */
 
-#include "lwip/if.h"
+#include "lwip/if_api.h"