Hearing Aid: codec and connection interval switching

Added support to switch the LE Connection Interval between 10 msec and
20 msec. Uses the "persist.bluetooth.hearingaid.interval" to configure.

Bug: 116317072
Bug: 116044083
Test: Manually use hearing aid devices and switches between 10 msec and
20 msec connection interval
Bug: 79579786
Change-Id: Iec15a0c9f76afe265368fd90662ffe60a29fb27b
Merged-In: I982002ac9a41969cda5dec73332b27b3142d7426