Surface ACL disconnect reasons from native to Java

HCI disconnect commands and events have an accompanying "reason"
parameter comprising of a HCI error code. This can be useful in both
debugging and re-connection logic at the Java level.

This CL grabs the HCI codes from native and passes it up to Java via an
extra parameter to existing ACL connection callbacks.

Tag: #feature
Bug: 177668957
Test: atest net_test_bluetooth # verify no regressions
Test: atest bluetoothtbd_test # verify no regressions
Test: atest bt_headless # verify test still builds
Test: manually disconnect local and remote devices and check logcats
from Java layer for disconnect reasons

Change-Id: Idcb1711345b515c5f60e55430352f5f4ff252d69