Ability to reference a packet's fields in another packet's fields description

class Test(Packet):
    fields_desc = [ IntField("test1",0),
                    SNAP,
                    IntField("test2",1) ]


>>> ls(SNAP)
OUI        : X3BytesField         = (0)
code       : XShortEnumField      = (0)
>>> ls(Test)
test1      : IntField             = (0)
OUI        : X3BytesField         = (0)
code       : XShortEnumField      = (0)
test2      : IntField             = (1)