CEC: Buffer Cec messages while allocating logical address

CEC messages arriving before logical address allocation was being
discarded. Handles them by introducing a message buffer class
to keep them till the address allocation is finished.

Also updated per-device message buffer to use copied version of
messages list for iterating to avoid the possible concurrent
modification exception.

Bug: 18896770
Change-Id: Ifb74fd265510de6dde322e0b3bc5b504fecb4daa