Keep in mind that this (like lxc/ docker) is not a supported configuration for running OpenWrt. OpenWrt relies on a number of kernel patches changing kernel behaviour (basically changing a bunch of sysctl settings) and expects to be able to load- and unloaded (its own-) kernel modules as required, neither of this can work within a container (but it would work on full system virtualization, like kvm, virtualbox, hyper-v, vmware, etc.).
While you will obviously get a shell that way, many things won't work and you will tear open a number of security issues (wrong/ unexpected sysctl configuration). and cause 'quirky' behaviour for the stations behind this router.
tl;dr: don't do it, really, don't.