allow ipv6 rules to be installed on ovs

When trying to install ipv6 rules either rules would be misinstalled 
For both rules that matched only on IPv6 (silent failure) or those that matched on IPv6 and nw_proto (WARNING:libopenflow_01:Fields ignored due to unspecified prerequisites: nw_proto), nw_proto and other wildcarded fields would be set zero.

E.g., cookie=0, duration_sec=36s, duration_nsec=396000000s, table_id=0, priority=60001, n_packets=0, n_bytes=0, idle_timeout=0,hard_timeout=0,dl_type=0x86dd,nw_tos=0x00,nw_proto=0,actions=