def collect_fields(self, fields, *layouts):
        pk_found = False
        for layout in layouts:
            for df in layout._store_fields:
                assert df is not None
                self.add_field_for(fields, df)
                if df.primary_key:
                    self.primary_keys.add(df)
                    pk_found = True
                    if self.pk is None:
                        self.pk = df

        if self.pk is None:
            self.pk = self.actor.get_pk_field()
        if self.pk is not None:
            if not pk_found:
                self.add_field_for(fields, self.pk)
Given an ll_type, retrieve the short name for the link layer.
dataset/ETHPy150Open lsaffre/lino/lino/core/store.py/Store.collect_fields--crossover with--dataset/ETHPy150Open kisom/pypcapfile/pcapfile/linklayer.py/slookup