port: init/free port on tarantool start/shutdown

Since we are going to rewrite func_adapter to use ports for arguments
and return values, submodule port must be initialized before `box.cfg{}`
because triggers are allowed to be used before database configuration.
So let's init and free port submodule in `box_init` and `box_free`
functions instead of `box_storage_init` and `box_storage_free` -
`box_storage` is initialized on `box.cfg{}` call.

NO_TEST=no behavior changes
NO_CHANGELOG=no behavior changes
NO_DOC=no behvior changes