Revert "dpif-netdev: includes microsecond delta in meter bucket calculation".

Revert "dpif-netdev: includes microsecond delta in meter bucket calculation".

This reverts commit 5c41c31ebd64fda821fb733a5784a7a440a794f8.

Use the pktgen-dpdk to test the commit 5c41c31ebd64
("dpif-netdev: includes microsecond delta in meter bucket calculation"),
it does't work as expected. And it broken the meter function (e.g. set
rate 200Mbps, the rate watched was 400Mbps). To reproduce it:

 $ ovs-vsctl add-br br-int -- set bridge br-int datapath_type=netdev
 $ ovs-ofctl -O OpenFlow13 add-meter br-int \
         "meter=100 kbps burst stats bands=type=drop rate=200000 burst_size=200000"
 $ ovs-ofctl -O OpenFlow13 add-flow br-int \
         "in_port=dpdk0 action=meter:100,output:dpdk1"
 $ pktgen -l 1,3,5,7,9,11,13,15,17,19 -n 8 --socket-mem 4096 \
         --file-prefix pg1 -w 0000:82:00.0 -w 0000:82:00.1 -- \
         -T -P -m "[3/5/7/9/11/13/15].[0-1]" -f meter-test.pkt

 meter-test.pkt:
 | set 0 count 0
 | set 0 size 1500
 | set 0 rate 100
 | set 0 burst 64
 | set 0 sport 1234
 | set 0 dport 5678
 | set 0 prime 1
 | set 0 type ipv4
 | set 0 proto udp
 | set 0 dst ip 1.1.1.2
 | set 0 src ip 1.1.1.1/24
 | set 0 dst mac ec:0d:9a:ab:54:0a
 | set 0 src mac ec:0d:9a:bf:df:bb
 | set 0 vlanid 0
 | start 0

Note that the issue that patch 5c41c31ebd64 was intended to fix was
already fixed by commit:
  42697ca7757b ("dpif-netdev: fix meter at high packet rate.")

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>