shared/shell: Enable generator for submenus

This enables command generator to work with submenu commands like:

[bluetooth]# advertise.
advertise.appearance    advertise.manufacturer  advertise.timeout
advertise.clear         advertise.name          advertise.tx-power
advertise.duration      advertise.service       advertise.uuids

Note that by default submenus commands will not be shown until . is
present in the input, that way only one command list is active at time.
1 file changed