This attribute points to a tag list of attribute mappings which the
icclass object uses to change the attribute ids of an om_update's
attribute/value pairs.  For example, if an icclass object had the
following ICA_MAP:

    struct TagItem map[] =
    {
        {PGA_Top, STRINGA_LongVal},
        {MYATTR, MYNEWATTR},
        {TAG_END, }
    };

before sending an om_update to its ica_target, the icclass object scans
through the om_update message's attribute/value pairs looking for the
pga_top and myattr attributes.  if it finds the pga_top attribute, it
changes PGA_Top to stringa_longval.  likewise, if the icclass object finds
the MYATTR attribute, it changes MYATTR to MYNEWATTR.  The icclass object
does not disturb the attribute's value.