Android Mainline Module Release 8848683,com.google.android.captiveportallogin,com.google.android.networkstack
Add obstack_printf to libobstack am: 5bef457686 am: c22026c70c am: ffe9223a19 am: eec863e7ee am: 4477a0b37a

Original change: https://android-review.googlesource.com/c/platform/external/obstack/+/1843836

Change-Id: I236b4fd7353785148c8feb0914cf18605a3e64e5