This implementation supports only IPv4.
* inet/ifaddrs.h: New file.
* sysdeps/generic/ifaddrs.c: New file.
* sysdeps/gnu/ifaddrs.c: New file.
* inet/test-ifaddrs.c: New file.
* inet/Makefile (routines): Add ifaddrs.
(headers): Add ifaddrs.h here.
(tests): Add test-ifaddrs.
* inet/Versions (GLIBC_2.3): New set, add getifaddrs and freeifaddrs.
* resolv/res_hconf.c (_res_hconf_reorder_addrs): Use an explicit
socket call to get an AF_INET socket, instead of using __opensock.
The SIOCGIFNETMASK ioctl will work only with a PF_INET socket.
* sysdeps/generic/ifreq.h (__ifreq): Take third argument SOCKFD,
if not -1 use it instead of calling __opensock.
* sysdeps/unix/sysv/linux/ifreq.h (__ifreq): Likewise.
* sysdeps/mach/hurd/ifreq.h (__ifreq): Take new argument and ignore it.
* resolv/res_hconf.c (_res_hconf_reorder_addrs): Pass new argument.
* sysdeps/mach/hurd/ifreq.h: New file.
* sysdeps/generic/ifreq.h (__if_freereq): Take second argument NUM_IFS.
* sysdeps/unix/sysv/linux/ifreq.h (__if_freereq): Likewise.
* resolv/res_hconf.c (_res_hconf_reorder_addrs): Update caller.
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