caliper: use common code for packet timeout

caliper: use common code for packet timeout

The previous implementation unconditionally waited for up to 1ms, and
optionally handled the user configured timeout period. Use common code
instead to handle the full span of the timeout period. Which somewhat
unclutters the .decode() routine's body by eliminating an unnecessary
step in the sequence. This change also reduces indentation, and prefers
Python's .format() over the old syntax.