LWIP PBUF_POOL_BUFSIZE increased to fit also IPv6 header

IPv6 header requires 20 more bytes compared to IPv4 header.

Author: Veijo Pesonen

features/FEATURE_LWIP/lwip-interface/lwipopts.h

@@ -150,6 +150,12 @@
 #ifdef MBED_CONF_LWIP_PBUF_POOL_BUFSIZE
 #undef PBUF_POOL_BUFSIZE
 #define PBUF_POOL_BUFSIZE           MBED_CONF_LWIP_PBUF_POOL_BUFSIZE
+#else
+#if LWIP_IPV6
+#define PBUF_POOL_BUFSIZE               LWIP_MEM_ALIGN_SIZE(TCP_MSS+20+40+PBUF_LINK_ENCAPSULATION_HLEN+PBUF_LINK_HLEN)
+#else
+#define PBUF_POOL_BUFSIZE               LWIP_MEM_ALIGN_SIZE(TCP_MSS+20+20+PBUF_LINK_ENCAPSULATION_HLEN+PBUF_LINK_HLEN)
+#endif
 #endif
 
 #ifdef MBED_CONF_LWIP_MEM_SIZE