net/udp: set ipv6 remote addr before udpip_hdrsize

In this case, remote addr is all zero, and the length of the
ip header is not recognized as ipv6_is_ipv4, This will cause
problems in subsequent data filling.

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

net/udp/udp_sendto_buffered.c

@@ -792,6 +792,7 @@ ssize_t psock_udp_sendto(FAR struct socket *psock, FAR const void *buf,
       else
         {
           memcpy(&wrb->wb_dest, to, tolen);
+          udp_connect(conn, to);
         }
 
       /* Skip l2/l3/l4 offset before copy */