Fix adbauth resetting the stack on unknown msg

Even though adbdauth and Framework ship together, flagging may result in
Framework sending unknown messages to adbdauth. In this case the message
should merely be discarded (and logged) instead of closing the socket
and losing all other sockets.

Test: adbd_auth_test
Bug: NA
Flag: EXEMPT (bug fix)
Change-Id: I6bfeeabd1db4c736cb4e84c17e8f96b23ccc1e0a