in6: fix conflict with glibc

in6: fix conflict with glibc

[ Upstream commit 6d08acd2d32e3e877579315dc3202d7a5f336d98 ]

Resolve conflicts between glibc definition of IPV6 socket options
and those defined in Linux headers. Looks like earlier efforts to
solve this did not cover all the definitions.

It resolves warnings during iproute2 build.
Please consider for stable as well.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>