ofp-util: Treat a packet-out in_port of OFPP_CONTROLLER as OFPP_NONE.

ofp-util: Treat a packet-out in_port of OFPP_CONTROLLER as OFPP_NONE.

Some OpenFlow 1.0 controllers incorrectly use OPFP_CONTROLLER as the
in_port in packet-out messages, when OFPP_NONE is their intent.  Until now,
Open vSwitch has rejected such requests with an error message.  This commit
makes Open vSwitch instead treat OFPP_CONTROLLER the same as OFPP_NONE for
compatibility with those controllers.

(Also, as of this writing, OpenFlow 1.0.1 appears to be changing the port
to use from OFPP_NONE to OFPP_CONTROLLER.)

Suggested-by: Rob Sherwood <rob.sherwood@bigswitch.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>