Fix netinet/in.h MCAST_* namespace (bug 18558).

Fix netinet/in.h MCAST_* namespace (bug 18558).

sysdeps/unix/sysv/linux/bits/in.h (as included in netinet/in.h, and
via that in netdb.h and arpa/inet.h) defines a series of MCAST_*
macros, both under __USE_MISC and then again unconditionally.  These
are not POSIX macros, nor in any of the namespaces listed in POSIX as
reserved for this header, so should not be defined unconditionally.
This patch duly removes the unconditional definitions, leaving the
ones conditional on __USE_MISC.

Tested for x86_64 and x86 (testsuite, and that installed stripped
shared libraries are unchanged by the patch).

	[BZ #18558]
	* sysdeps/unix/sysv/linux/bits/in.h (MCAST_JOIN_GROUP): Remove
	unconditional definition.
	(MCAST_BLOCK_SOURCE): Likewise.
	(MCAST_UNBLOCK_SOURCE): Likewise.
	(MCAST_LEAVE_GROUP): Likewise.
	(MCAST_JOIN_SOURCE_GROUP): Likewise.
	(MCAST_LEAVE_SOURCE_GROUP): Likewise.
	(MCAST_MSFILTER): Likewise.
	* conform/Makefile (test-xfail-XOPEN2K/arpa/inet.h/conform):
	Remove variable.
	(test-xfail-XOPEN2K/netdb.h/conform): Likewise.
	(test-xfail-XOPEN2K/netinet/in.h/conform): Likewise.
	(test-xfail-XOPEN2K8/arpa/inet.h/conform): Likewise.
	(test-xfail-XOPEN2K8/netdb.h/conform): Likewise.
	(test-xfail-XOPEN2K8/netinet/in.h/conform): Likewise.