bridge: Move packet processing functionality into ofproto.

bridge: Move packet processing functionality into ofproto.

Until now, packet processing in ovs-vswitchd has been split between two
components: ofproto, for basic OpenFlow functionality, and bridge, for
OFPP_NORMAL processing.  This architecture will not work as Open vSwitch
starts to support a wider variety of underlying hardware, because it
imposes a model in which the bridge needs to be able to look at every
exact-match flow within a OpenFlow flow, which most hardware doesn't
support.

Therefore, this commit moves all of the packet processing code in
bridge into ofproto, as preparation for generalizing further.