Resolve compilation errors and implement blocking API

src/tcp.h

@@ -26,15 +26,6 @@ typedef struct {
     int tag;
 } Event;
 
-typedef struct {
-    union {
-        IPv4 ipv4;
-        IPv6 ipv6;
-    };
-    bool is_ipv4;
-    uint16_t port;
-} Address;
-
 typedef struct {
     SOCKET    fd;
     int       tag;