Minor: Add macros to map/unmap IPv6 mapped IPv4 addresses

src/include/lwip/ip_addr.h

@@ -215,6 +215,16 @@ int ipaddr_aton(const char *cp, ip_addr_t *addr);
 /** @ingroup ipaddr */
 #define IPADDR_STRLEN_MAX   IP6ADDR_STRLEN_MAX
 
+#define ip4_2_ipv6_mapped_ipv4(ip6addr, ip4addr) do { \
+  (ip6addr)->addr[0] = 0; \
+  (ip6addr)->addr[1] = 0; \
+  (ip6addr)->addr[2] = PP_HTONL(0x0000FFFFUL); \
+  (ip6addr)->addr[3] = (ip4addr)->addr; } while(0);
+
+#define unmap_ipv6_mapped_ipv4(target, source) do { \
+  (target)->u_addr.ip4.addr = (source)->u_addr.ip6.addr[3]; \
+  (target)->type = IPADDR_TYPE_V4; } while(0);
+
 #else /* LWIP_IPV4 && LWIP_IPV6 */
 
 #define IP_ADDR_PCB_VERSION_MATCH(addr, pcb)         1