Read connection intervals from config.xml so it can be overriden by device.

Wear needs the minimum possible connection interval for BLE connections
to support the Wear iOS companion app. This change simply moves the hard-
coded connection intervals to config.xml so they can be overriden for
Wear devices.

Bug: 23903184
Change-Id: I1f60772ef6a100ad5e4f02f629b5ca6e80fc207a