daemon: systemd socket activation
http://0pointer.de/blog/projects/socket-activation.html
As in labs/knot#325
Steps:
-
Add optional dependency on systemd in Makefile -
Add -DHAS_SYSTEMD to CFLAGS depending on the outcome (Makefile) -
Add unit test for this (with mocked systemd) -
Add the ability to pass fds over parameters --fd=
-
Add socket activation in main()
guarded by#if HAS_SYSTEMD