pkt_sched: sch_htb: Remove L2T()

L2T() is currently used only in one place (and has one spurious
parameter, btw), so let's: 'get rid of L2T completely, and just
use "qdisc_l2t(rate, size)" directly.' - quote & feedback from
David S. Miller.

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>