Remove getifaddrs from the "not yet" category. (#1562)

`getifaddrs` is also in the `higher level" category, which appears
to be the more appropriate.

Author: sunfishcode

src/not_implemented.rs

@@ -297,7 +297,6 @@ pub mod yet {
     not_implemented!(cachestat);
     not_implemented!(fanotify_init);
     not_implemented!(fanotify_mark);
-    not_implemented!(getifaddrs);
     not_implemented!(signalfd);
     not_implemented!(mount_setattr);
     not_implemented!(extattr_delete_fd);