oci/caps: improve error message for unsupported capabilities
oci/caps: improve error message for unsupported capabilities

A capability can either be invalid, or not supported by the kernel
on which we're running. This patch changes the error message produced
to reflect if the capability is invalid/unknown, or a known capability,
but not supported by the kernel version.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

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