blktrace: add support for non-native endian format

blktrace: add support for non-native endian format

The blktrace format is stored in the native endianness of
the machine it is run on. So to reply traces on a machine
with a different endianness, we need to swap the trace
fields. Detect and do this automatically.

Signed-off-by: Jens Axboe <axboe@kernel.dk>