Fix getifaddrs, freeifaddrs namespace (bug 17668).

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.