Always ACK indications in the event of an error

This works around a race condition in which the just-connected remote
device sends the local device an indication before the appropriate
handle/device/etc. has been added to the cache.  Previously we were
dropping that indication, which led to the remote device timing out
and disconnecting some time after the connection had been successfully
established.

Bug: 21026847

Change-Id: Iea43e7c93e48b5e7a7e78a1c3fb591d6fe972fc3