IPv6 project is started.

1. Remove thread lock in select loop.
2. Nonblocking will be used in select loop for good performance.
3. Connection mode for UDP socket & SCTP(SEQPACKET)

More test is needed.

lib/core/include/core_tcp.h

@@ -0,0 +1,20 @@
+#ifndef __CORE_TCP_H__
+#define __CORE_TCP_H__
+
+#include "core_sock.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+CORE_DECLARE(status_t) tcp_create(sock_id *new,
+        int family,
+        const char *local_host, c_uint16_t local_port,
+        const char *remote_host, c_uint16_t remote_port,
+        int flags);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif