Add a TODO in the Dockerfile regarding nftables
Add a TODO in the Dockerfile regarding nftables

Someday, we'll hopefully support nftables directly and will likely then need some kind of in-container runtime detection (perhaps based on loaded modules or something similar).  This updates the related `Dockerfile` comment accordingly (linking to the appropriate `nftables` tracking issue).

Signed-off-by: Tianon Gravi <4b2b69742da531f1900c4c4748d7a0ecda59626a@gmail.com>

jimjag/docker,konstruktoid/docker-1,Mokolea/docker,trebonian/docker,bearstech/moby,AkihiroSuda/docker,Ramzec/docker,gnailuy/docker,flavio/docker,mahak/docker,moul/docker,konstruktoid/docker-upstream,Mokolea/docker,yosifkit/docker,bearstech/moby,trebonian/docker,trebonian/docker,Ramzec/docker,paralin/docker,kojiromike/docker,bearstech/moby,yosifkit/docker,thaJeztah/docker,flavio/docker,jvanz/docker,nalind/docker,cpuguy83/docker,cpuguy83/docker,gnailuy/docker,cpuguy83/docker,trebonian/docker,konstruktoid/docker-upstream,docker/docker,jimjag/docker,konstruktoid/docker-upstream,ibuildthecloud/docker,jvanz/docker,mahak/docker,AkihiroSuda/docker,Ramzec/docker,paralin/docker,flavio/docker,konstruktoid/docker-1,flavio/docker,estesp/docker,docker/docker,Mokolea/docker,justincormack/docker,nalind/docker,paralin/docker,djs55/docker,nawawi/docker,jimjag/docker,moul/docker,justincormack/docker,yosifkit/docker,vdemeester/docker,bearstech/moby,jvanz/docker,djs55/docker,moby/moby,ibuildthecloud/docker,AkihiroSuda/docker,jimjag/docker,AkihiroSuda/docker,kojiromike/docker,nalind/docker,docker/docker,jthelin/docker,estesp/docker,dims/docker,konstruktoid/docker-upstream,nawawi/docker,moul/docker,gnailuy/docker,moby/moby,moul/docker,moby/moby,paralin/docker,thaJeztah/docker,dims/docker,estesp/docker,kojiromike/docker,cpuguy83/docker,nawawi/docker,yosifkit/docker,justincormack/docker,thaJeztah/docker,jthelin/docker,moby/moby,gnailuy/docker,Ramzec/docker,thaJeztah/docker,Mokolea/docker,dims/docker,ibuildthecloud/docker,vdemeester/docker,vdemeester/docker,ibuildthecloud/docker,nalind/docker,jameszhan/docker,mahak/docker,jameszhan/docker,ibuildthecloud/docker,mahak/docker,jameszhan/docker,konstruktoid/docker-1,djs55/docker,nawawi/docker