Fix getifaddrs, freeifaddrs namespace (bug 17668).

Various objects in glibc bring in ifaddrs.o (via references to
__netlink_*) and thereby getifaddrs and freeifaddrs, which are not
part of any standard supported by glibc.  These should be weak aliases
of __getifaddrs and __freeifaddrs; this patch makes them so.

(The path by which these functions are brought in is Linux-specific,
but it seems less confusing to make all versions of these functions
weak aliases rather than only the Linux-specific versions that
definitely need it.)

Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by this patch).

	[BZ #17668]
	* inet/ifaddrs.c (getifaddrs): Rename to __getifaddrs and define
	as weak alias of __getifaddrs.  Use libc_hidden_weak.
	(freeifaddrs): Rename to __freeifaddrs and define as weak alias of
	__freeifaddrs.  Use libc_hidden_weak.
	* sysdeps/gnu/ifaddrs.c (getifaddrs): Rename to __getifaddrs and
	define as weak alias of __getifaddrs.  Use libc_hidden_weak.
	(freeifaddrs): Rename to __freeifaddrs and define as weak alias of
	__freeifaddrs.  Use libc_hidden_weak.
	* sysdeps/unix/sysv/linux/ifaddrs.c (getifaddrs): Rename to
	__getifaddrs and define as weak alias of __getifaddrs.  Use
	libc_hidden_weak.
	(freeifaddrs): Rename to __freeifaddrs and define as weak alias of
	__freeifaddrs.  Use libc_hidden_weak.
	* conform/Makefile (test-xfail-XOPEN2K/net/if.h/linknamespace):
	Remove variable.
	(test-xfail-POSIX2008/net/if.h/linknamespace): Likewise.
	(test-xfail-XOPEN2K8/net/if.h/linknamespace): Likewise.
Remove some linknamespace test XFAILs.

It seems two of the XFAILed linknamespace tests were completely fixed
by some of my recent namespace fixes in combination (although not by
any individual one of those fixes relative to the sources used for
testing each patch, or that individual fix would also have removed the
XFAIL in question).  This patch removes those XFAILs that are no
longer needed.

Tested for x86_64.

	* conform/Makefile (test-xfail-XOPEN2K/aio.h/linknamespace):
	Remove variable.
	(test-xfail-XOPEN2K8/aio.h/linknamespace): Likewise.