Change hamlib_port_t to a pointer in rig.state
Deprecate static hamlib_port_t structure
New hamlib_port_t structure at end of rig.state
Clients built with older hamlib will use old structure in DLL
Clients built with newer hamlib will use new structure in DLL
So we maintain backwards compatibility until Hamlib 5.0
https://github.com/Hamlib/Hamlib/issues/894