Add vrf counter request/reply.

Add OFP_BSN_VLAN_ALL constant to request counters for all vlans.
OFP_BSN_VRF_ALL should be 32 bits in length.
Change wire_type of VRF_ALL to uint32_t.
Merge into master from pull request #291:
Add vrf counter request/reply. (https://github.com/floodlight/loxigen/pull/291)