of14: Add OFPTableModProp serialization

This will be used by at least the serialisation of
flow mod messages with properties.

Signed-off-by: Simon Horman <horms@verge.net.au>

---
v2
* first post
of14: Add properties support to flow mod

With this change the initialiser of OFPTableMod now
requires a properties argument. This is incompatible with
Ryu v3.6. If it is important to maintain compatibility
then things can be reworked a little to make the properties
argument optional.

Signed-off-by: Simon Horman <horms@verge.net.au>

---
v2
* first post
of14: table mod with properties

Signed-off-by: Simon Horman <horms@verge.net.au>

---
v2
* first post