If the buffer contains padding at the end, the iteration must continue
in order to restart iteration from the start of the buffer.
genodelabs/genode#4244
Both, trace_logger and vfs_trace had their own trace_buffer.h. This
commit consolidates the existing implementations and provides the
resulting trace_buffer.h at 'include/trace/'. It thereby becomes part of
the trace api archive.
genodelabs/genode#4244
