TCP_Flag extension model additions for OFPXMC_NXM_1 class

Patch2: changed model descrip to be more generic to better
represent the high level model.

Patch1: Modified the high level models
opendaylight-match-types.yang and
opendaylight-table-types.yang to support TCP_Flag reads.

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

Change-Id: Ia80e9014efa02bdb52dffeb1620625103e8dd985
Signed-off-by: Brent Salisbury <brent.salisbury@gmail.com>