Since /etc/network/if-up.d seem not to get executed when connection is bougth up. I moved my script that handles tc rules in '/etc/networkd-dispatcher/routable.d'.

During boot it throws me error:
Code:
$ journalctl -b -u networkd-dispatcher
May 06 06:37:04 phobos systemd[1]: Starting networkd-dispatcher.service - Dispatcher daemon for systemd-networkd...
May 06 06:37:04 phobos networkd-dispatcher[2370]: No valid path found for iw
May 06 06:37:04 phobos networkctl[2579]: systemd-networkd is not running, output might be incomplete.
May 06 06:37:04 phobos systemd[1]: networkd-dispatcher.service: Got notification message from PID 2579, but reception only permitted for main PID 2370
May 06 06:37:04 phobos networkd-dispatcher[2370]: ERROR:Unknown state for interface NetworkctlListState(idx=1, name='lo', type='loopback', operational='-', administrative='unmanaged'): -
May 06 06:37:04 phobos networkd-dispatcher[2370]: Traceback (most recent call last):
May 06 06:37:04 phobos networkd-dispatcher[2370]:   File "/usr/bin/networkd-dispatcher", line 299, in trigger_all
May 06 06:37:04 phobos networkd-dispatcher[2370]:     self.handle_state(iface_name,
May 06 06:37:04 phobos networkd-dispatcher[2370]:   File "/usr/bin/networkd-dispatcher", line 349, in handle_state
May 06 06:37:04 phobos networkd-dispatcher[2370]:     raise UnknownState(operational_state)
May 06 06:37:04 phobos networkd-dispatcher[2370]: UnknownState: -
May 06 06:37:04 phobos networkd-dispatcher[2370]: ERROR:Unknown state for interface NetworkctlListState(idx=2, name='enp3s0', type='ether', operational='-', administrative='unmanaged'): -
May 06 06:37:04 phobos networkd-dispatcher[2370]: Traceback (most recent call last):
May 06 06:37:04 phobos networkd-dispatcher[2370]:   File "/usr/bin/networkd-dispatcher", line 299, in trigger_all
May 06 06:37:04 phobos networkd-dispatcher[2370]:     self.handle_state(iface_name,
May 06 06:37:04 phobos networkd-dispatcher[2370]:   File "/usr/bin/networkd-dispatcher", line 349, in handle_state
May 06 06:37:04 phobos networkd-dispatcher[2370]:     raise UnknownState(operational_state)
May 06 06:37:04 phobos networkd-dispatcher[2370]: UnknownState: -
May 06 06:37:04 phobos networkd-dispatcher[2370]: ERROR:Unknown state for interface NetworkctlListState(idx=3, name='wlp0s20f3', type='wlan', operational='-', administrative='unmanaged'): -
May 06 06:37:04 phobos networkd-dispatcher[2370]: Traceback (most recent call last):
May 06 06:37:04 phobos networkd-dispatcher[2370]:   File "/usr/bin/networkd-dispatcher", line 299, in trigger_all
May 06 06:37:04 phobos networkd-dispatcher[2370]:     self.handle_state(iface_name,
May 06 06:37:04 phobos networkd-dispatcher[2370]:   File "/usr/bin/networkd-dispatcher", line 349, in handle_state
May 06 06:37:04 phobos networkd-dispatcher[2370]:     raise UnknownState(operational_state)
May 06 06:37:04 phobos networkd-dispatcher[2370]: UnknownState: -
May 06 06:37:04 phobos systemd[1]: Started networkd-dispatcher.service - Dispatcher daemon for systemd-networkd.
Doing 'ip link set enp3s0 down/up' however works after boot.

So seems it tries to get state before interface is up or something?