Fix HCI parser and packetizer

Issue found from the test H4ProtocolAsyncTest#TestMultiplePackets.
The packetizer does not correctly handle a packet termination
at the beginning of a chunk.

Test: atest --host bluetooth-vendor-interface-hci-test
Bug: 276652301
Change-Id: I1b61efcfa5f817fdb8b5870e81d660be5279fdea
3 files changed