external/okhttp changes to support connection pool flushing

When the preferred network / default network for a device
changes we must flush any pooled connections.

This change has a known issue which will be fixed in a
later commit: Any connections that are in use when
the pool is cleared can be put (back) into the pool after
evictAll(). This means those connections will continue to
reference the old preferred / default network.

Bug: 17314604

(cherry-picked from commit 84f674f3abba1083e1efd94520d516036a3f0b6a)

Change-Id: Ib5dbeb5a90aff68da3dd312f924c2bdb44f6f213
Merge "external/okhttp changes to support connection pool flushing"