Creating a pointer at port structure to integrate with ns3 ports.
Revert "Removing one more static modifier."

This reverts commit a90b6f1cd006dbc426e05b605726335ca7cd07ba.
Reverting back some static modifiers.
Skipping an unnecessary (and problematic) check to avoid reimplement entire function.
Defining dp_ports_output as weak function, allowing ns3 to override it.