sch_tbf: Remove holes in struct tbf_sched_data.

On x86_64 we have 3 holes in struct tbf_sched_data.

The member peak_present can be replaced with peak.rate_bytes_ps,
because peak.rate_bytes_ps is set only when peak is specified in
tbf_change(). tbf_peak_present() is introduced to test
peak.rate_bytes_ps.

The member max_size is moved to fill 32bit hole.

Signed-off-by: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>