Allow send_flow_mod() to send NXTFlowMod messages in place of OFPFlowMod
messages if the match includes fields chat can't be encoded by OFPMatch
The flow format will be upgraded as necessary
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>