Improve LWIP for Renesas

For speeding up of LWIP in RZ/A1, I added four new config processes in mbed_lib.json and lwipopts.h, overriden those values.
Since RZ/A1 incorporates a large memory, can actualize speeding up by running with the override value.
Also those new config processes will be helpful for more customize.

features/lwipstack/lwipopts.h

@@ -139,6 +139,26 @@
 
 #define LWIP_RAM_HEAP_POINTER       lwip_ram_heap
 
+// Number of simultaneously queued TCP segments.
+#ifdef MBED_CONF_LWIP_MEMP_NUM_TCP_SEG
+#define MEMP_NUM_TCP_SEG            MBED_CONF_LWIP_MEMP_NUM_TCP_SEG
+#endif
+
+// TCP Maximum segment size.
+#ifdef MBED_CONF_LWIP_TCP_MSS
+#define TCP_MSS                     MBED_CONF_LWIP_TCP_MSS
+#endif
+
+// TCP sender buffer space (bytes).
+#ifdef MBED_CONF_LWIP_TCP_SND_BUF
+#define TCP_SND_BUF                 MBED_CONF_LWIP_TCP_SND_BUF
+#endif
+
+// TCP sender buffer space (bytes).
+#ifdef MBED_CONF_LWIP_TCP_WND
+#define TCP_WND                     MBED_CONF_LWIP_TCP_WND
+#endif
+
 // Number of pool pbufs.
 // Each requires 684 bytes of RAM (if MSS=536 and PBUF_POOL_BUFSIZE defaulting to be based on MSS)
 #ifdef MBED_CONF_LWIP_PBUF_POOL_SIZE

features/lwipstack/mbed_lib.json

@@ -72,6 +72,22 @@
             "help": "Maximum number of open UDPSocket instances allowed, including one used internally for DNS.  Each requires 84 bytes of pre-allocated RAM",
             "value": 4
         },
+        "memp-num-tcp-seg": {
+            "help": "Number of simultaneously queued TCP segments. Current default (used if null here) is set to 16 in opt.h, unless overridden by target Ethernet drivers.",
+            "value": null
+        },
+        "tcp-mss": {
+            "help": "TCP Maximum segment size. Current default (used if null here) is set to 536 in opt.h, unless overridden by target Ethernet drivers.",
+            "value": null
+        },
+        "tcp-snd-buf": {
+            "help": "TCP sender buffer space (bytes). Current default (used if null here) is set to (2 * TCP_MSS) in opt.h, unless overridden by target Ethernet drivers.",
+            "value": null
+        },
+        "tcp-wnd": {
+            "help": "TCP sender buffer space (bytes). Current default (used if null here) is set to (4 * TCP_MSS) in opt.h, unless overridden by target Ethernet drivers.",
+            "value": null
+        },
         "pbuf-pool-size": {
             "help": "Number of pbufs in pool - usually used for received packets, so this determines how much data can be buffered between reception and the application reading. If a driver uses PBUF_RAM for reception, less pool may be needed. Current default (used if null here) is set to 5 in lwipopts.h, unless overridden by target Ethernet drivers.",
             "value": null
@@ -132,6 +148,11 @@
             "tcpip-thread-stacksize": 1328,
             "default-thread-stacksize": 640,
             "ppp-thread-stacksize": 896,
+            "memp-num-tcp-seg": 32,
+            "tcp-mss": 1460,
+            "tcp-snd-buf": "(8 * TCP_MSS)",
+            "tcp-wnd": "(TCP_MSS * 8)",
+            "pbuf-pool-size": 16,
             "mem-size": 51200
         }
     }