Implement getifaddrs(3)/freeifaddrs(3).

Time to dust off the old libcore implementation from gingerbread and add it
to bionic. Unlike the original, this actually looks at both RTM_NEWLINK and
RTM_NEWADDR.

Bug: http://b/26238832
Change-Id: I7bb4b432deb766065b66b9c9ff36ed68249aba82
diff --git a/libc/Android.mk b/libc/Android.mk
index a399b89..83e1fb5 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -149,6 +149,7 @@
     bionic/getpid.cpp \
     bionic/gettid.cpp \
     bionic/__gnu_basename.cpp \
+    bionic/ifaddrs.cpp \
     bionic/inotify_init.cpp \
     bionic/ioctl.cpp \
     bionic/lchown.cpp \