Move IPPROTO_IPV6 from #ifdef __BSD_VISIBLE to #if __POSIX_VISIBLE >= 201112 since POSIX 2001 states that it shall be defined.
Move IPPROTO_IPV6 from #ifdef __BSD_VISIBLE to #if __POSIX_VISIBLE >= 201112
since POSIX 2001 states that it shall be defined.

Reported by:	sbruno
Reviewed by:	jilles
MFC after:	1 week

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