Move more stuff to libcfnet, get rid of some thread-unsafe code

* Moved AgentConnection to libcfnet, which caused inclusion of cfnet.h from
  many files.

* Removed cf3.defs.h dependency from most of libcfnet, network specific
  defines were moved to cfnet.h.

* Removed sockaddr.c and replaced the thread-unsafe sockaddr_{pton,ntop}
  functions with inet_{pton,ntop} from POSIX.
  * TODO replacement functions for platforms missing them.