Request all tethering interfaces, fix corruption.

netd now tracks statistics for tethered interfaces across tethering
sessions, so switch to asking for all tethering stats.  (Currently
we're double-counting all tethering data, ever since it started
tracking across sessions.)

Also catch OOME to handle corrupt stats files, which we then dump to
DropBox and then start over.

Bug: 5868832, 9796109
Change-Id: I2eb2a1bf01b993dd198597d770fe0e022466c6b9