net/soerr: add new _SO_CONN_SETERRNO() macro

support so error code set from conn instance

Signed-off-by: chao an <anchao@xiaomi.com>

net/socket/net_sendfile.c

@@ -133,8 +133,7 @@ ssize_t psock_sendfile(FAR struct socket *psock, FAR struct file *infile,
 
   if (ret < 0)
     {
-      FAR struct socket_conn_s *conn = psock->s_conn;
-      conn->s_error = -ret;
+      _SO_SETERRNO(psock, -ret);
     }
 
   return ret;