Add REST APIs for flow filter.

Note that flow filter feature is not yet implemented.
Currently all flow filter REST APIs do nothing.

Change-Id: Ic6a3e65355e8162b8e19df6320008cecab209d0f
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>
Merge "Add REST APIs for flow filter."