rootless: set systemd KillMode to mixed
rootless: set systemd KillMode to mixed

Now `systemctl --user stop docker` completes just with in 1 or 2 seconds.

Fix issue 41944 ("Docker rootless does not exit properly if containers are running")

See systemd.kill(5) https://www.freedesktop.org/software/systemd/man/systemd.kill.html

Signed-off-by: Akihiro Suda <10ddef0dea2a66ab193b07198faa879adcb213d8@hco.ntt.co.jp>

mahak/docker,trebonian/docker,nalind/docker,bearstech/moby,jimjag/docker,yosifkit/docker,Ramzec/docker,thaJeztah/docker,bearstech/moby,AkihiroSuda/docker,flavio/docker,moul/docker,yosifkit/docker,nalind/docker,nawawi/docker,docker/docker,Mokolea/docker,nalind/docker,thaJeztah/docker,cpuguy83/docker,flavio/docker,Ramzec/docker,paralin/docker,jameszhan/docker,konstruktoid/docker-upstream,kojiromike/docker,AkihiroSuda/docker,paralin/docker,docker/docker,vdemeester/docker,yosifkit/docker,nawawi/docker,gnailuy/docker,moul/docker,moby/moby,docker/docker,gnailuy/docker,trebonian/docker,Mokolea/docker,djs55/docker,gnailuy/docker,kojiromike/docker,bearstech/moby,jameszhan/docker,vdemeester/docker,Mokolea/docker,djs55/docker,jameszhan/docker,flavio/docker,mahak/docker,cpuguy83/docker,konstruktoid/docker-upstream,Mokolea/docker,trebonian/docker,moby/moby,yosifkit/docker,paralin/docker,AkihiroSuda/docker,jimjag/docker,moby/moby,djs55/docker,cpuguy83/docker,paralin/docker,trebonian/docker,jthelin/docker,moby/moby,nalind/docker,flavio/docker,mahak/docker,jthelin/docker,moul/docker,mahak/docker,moul/docker,nawawi/docker,cpuguy83/docker,konstruktoid/docker-upstream,AkihiroSuda/docker,nawawi/docker,Ramzec/docker,thaJeztah/docker,bearstech/moby,kojiromike/docker,vdemeester/docker,konstruktoid/docker-upstream,jimjag/docker,Ramzec/docker,thaJeztah/docker,gnailuy/docker,jimjag/docker