Update netinet/tcp.h from Linux 4.18

[Florian Weimer]

On 08/17/2018 06:22 PM, Joseph Myers wrote:
> 2018-08-17  Joseph Myers<joseph@codesourcery.com>
> 
> 	* sysdeps/gnu/netinet/tcp.h (TCP_ZEROCOPY_RECEIVE): New macro.
> 	(TCP_INQ): Likewise.
> 	(TCP_CM_INQ): Likewise.
> 	(TCP_REPAIR_ON): Likewise.
> 	(TCP_REPAIR_OFF): Likewise.
> 	(TCP_REPAIR_OFF_NO_WP): Likewise.
> 	(struct tcp_zerocopy_receive): New type.

The definitions are okay.

> +struct tcp_zerocopy_receive
> +{
> +  uint64_t address; /* Address of mapping.  */
> +  uint32_t length; /* Number of bytes to map/mapped.  */
> +  uint32_t recv_skip_hint; /* Amount of bytes to skip.  */
> +};

I'm not sure if the field comments are helpful because the in/out 
information is missing.

Thanks,
Florian