ofproto: Reject invalid input ports in OFPT_PACKET_OUT requests.

ofproto: Reject invalid input ports in OFPT_PACKET_OUT requests.

Some invalid ports (those above the maximum port number supported by the
datapath, including OpenFlow reserved ports that are not translated by OVS
into some other number) will be rejected by the datapath.  It's better to
catch these early and send back an appropriate OpenFlow error code, rather
than to just get EINVAL from the kernel and have to guess at the problem.

Reported-by: Aaron Rosen <arosen@clemson.edu>