fabric: Add size field to ops structures

Basically revert commit 3c4c4e21b169e5490989767660a5b1e8d70d7bca.
Add a size field to all ops structures.  This will allow
extensions to the ops structures in a compatible manner.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Merge pull request #56 from shefty/master

fabric: Add size field to ops structures