Added augmentations for TCP_Flag reads and low level models

Extensions are supered under OFPXMC_NXM_1 code point 0x0001

Once this and the high-level controller patches merge
I will commit the openflowplugin conversion patch since
openflowplugin will fail its build until the yang bindings
are generated.

Signed-off-by: Brent Salisbury <brent.salisbury@gmail.com>