When using vsock in stream mode (or any other stream mode connection)
message boundaries are not preserved, so the original messages can get
both split and merged. The TEST_MESSAGE and TEST_TEXT messages don't
have a length field which makes it imposible to support every possible
message that can be sent over a channel that preserves message
boundaries. Since the current message header types don't contain any
printable character, we assume any of these characters in a message
payload means that two messages got merged, so we split them back up.
Additionally, if we receive a message that does not start with a valid
message header, we assume it is a continuation of the previous message.
Test: trusty-ut-ctrl -D VSOCK:2:1 com.android.libctest ^Z fg
Bug: 298705967
Change-Id: I0e470a23664268f86e4defd824c47be3479c8f25
f29f1a2a38