swim: Rename struct SWIM to Swim

swim: Rename struct SWIM to Swim

Currently we have a SWIM typedef and a SWIM type checking macro,
but OBJECT_DECLARE* would transform the SWIM macro into a
function, and the function name would conflict with the SWIM
typedef name.

Rename the struct and typedef to "Swim". This will make future
conversion to OBJECT_DECLARE* easier.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Laurent Vivier <laurent@vivier.eu>
Tested-By: Roman Bolshakov <r.bolshakov@yadro.com>
Message-Id: <20200825192110.3528606-50-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>