[FIX] expression: fix missing results in direct search on many2many fields

This case corresponds to searches like `[(field, 'ilike', name)]` where `field`
is a many2many field.  The domain processing performs a `name_search` on the
field's comodel, then makes the relation match the returned record ids.

Problem: the call to `name_search` uses the default limit (100), and this makes
the search return less results than expected.  Make the search complete by
forcing `limit=None`.