Use systemd notify system to start daemon and give status.

Various fixes

Use splice instead of copy.

- SO_REUSEADDR wasn't set most of the time since it was depending
  on uninitialized optval.

- BUF_SIZE was less than MTU resulting in sub-optimal performance, 16384
  is even more than enough to accomodate Jumbo Frames.
- Sockets weren't closed in the event of a failure to connect to remote.
- Fixed some compiler warnings about invalid data types.