This patch adds the new constants UDP_NO_CHECK6_TX and
UDP_NO_CHECK6_RX from Linux 3.16 to sysdeps/gnu/netinet/udp.h. (I
believe the existing constants there are already Linux-specific,
possibly with the intention that other OSes should adopt the same
values if possible if adopting the features in question.)
Tested on x86_64.
* sysdeps/gnu/netinet/udp.h (UDP_NO_CHECK6_TX): New macro.
(UDP_NO_CHECK6_RX): Likewise.