'Removes unmatchable fields
The logic in this should exactly match that in _wire_wildcards()'

def fix(self):

    if (self.dl_type == 2048):
        if (self.nw_proto not in (1, 6, 17)):
            self.tp_src = None
            self.tp_dst = None
            return
    elif (self.dl_type == 2054):
        self.tp_src = None
        self.tp_dst = None
        self.nw_tos = None
        return
    else:
        self.nw_tos = None
        self.nw_proto = None
        self.nw_src = None
        self.nw_dst = None
        self.tp_src = None
        self.tp_dst = None
        return
