'check is interface vbdif is valid'

def is_valid_vbdif(self, ifname):

    if (not ifname.upper().startswith('VBDIF')):
        return False
    bdid = self.vbdif_name.replace('    ', '').upper().replace('VBDIF', '')
    if (not bdid.isdigit()):
        return False
    if ((int(bdid) < 1) or (int(bdid) > 16777215)):
        return False
    return True
