net_sched: htb: support of 64bit rates

HTB already can deal with 64bit rates, we only have to add two new
attributes so that tc can use them to break the current 32bit ABI
barrier.

TCA_HTB_RATE64 : class rate  (in bytes per second)
TCA_HTB_CEIL64 : class ceil  (in bytes per second)

This allows us to setup HTB on 40Gbps links, as 32bit limit is
actually ~34Gbps

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>