Enhance sock_addr_local syscall (#1320)

Slightly change the __wasi_sock_addr_local interface - since we already have
a `__wasi_addr_t` structure which is an union, there's no need for passing the
length around - the address buffer will always have the right length (i.e. max
of all address families).

core/shared/platform/include/platform_api_extension.h

@@ -374,6 +374,25 @@ os_socket_addr_resolve(const char *host, const char *service,
                        bh_addr_info_t *addr_info, size_t addr_info_size,
                        size_t *max_info_size);
 
+/**
+ * Returns an binary address and a port of the local socket
+ *
+ * @param socket the local socket
+ *
+ * @param buf buffer to store the address
+ *
+ * @param buflen length of the buf buffer
+ *
+ * @param port a buffer for storing socket's port
+ *
+ * @param is_ipv4 a buffer for storing information about the address family
+ *
+ * @return On success, returns 0; otherwise, it returns -1.
+ */
+int
+os_socket_addr_local(bh_socket_t socket, uint8_t *buf, size_t buflen,
+                     uint16_t *port, uint8_t *is_ipv4);
+
 #ifdef __cplusplus
 }
 #endif