Bluetooth: Mesh: Shell: fix vnd model pub command

The command at most takes 11 args. argc = num of args + 1 (command
name) => 12. We substruct 3 from argc (cmd name, mod id, addr). This
gives argc = 9 when all args are provided for vendor model.

Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>