openvswitch: Simplify mega-flow APIs.

Hides mega-flow implementation in flow_table.c rather than
datapath.c.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>

diff --cc net/openvswitch/datapath.c
Simple merge

diff --cc net/openvswitch/flow_table.c
Simple merge

diff --cc net/openvswitch/flow_table.h
Simple merge