ofproto-dpif: Fix bond accounting.

ofproto-dpif: Fix bond accounting.

Calls to bond_account() and bond_choose_output_slave() had different ideas
for the vlan of a flow that did not have a tagged VLAN.  The call to
bond_choose_output_slave() passed OFP_VLAN_NONE in this case, the call to
bond_account() passed 0.  This meant that packets not on a VLAN weren't
accounted properly, which typically caused bond/show to show "0 kB load"
on active hashes.  Obviously that broke rebalancing too.

I've verified that this fixes accounting.  I haven't directly verified that
it fixes rebalancing, so it's possible that there is another issue too.

Reported-by: Michael Mao <mmao@nicira.com>