fixes #7802, when api version 1.11 is `json.Marshal`ing the container struct

Signed-off-by: Jessica Frazelle <jfrazelle@users.noreply.github.com>

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jfrazelle@users.noreply.github.com> (github: )
Merge pull request #7914 from jfrazelle/7802-backwards-compat-state

fixes #7802, when api version 1.11 is `json.Marshal`ing the container st...