Fix map offsets in the "masterformat" system test

Fix map offsets in the "masterformat" system test

The "masterformat" system test attempts to check named-checkzone
behavior when it is fed corrupt map-format zone files.  However, despite
the RBTDB and RBT structures having evolved over the years, the offsets
at which a valid map-format zone file is malformed by the "masterformat"
test have not been updated accordingly, causing the relevant checks to
introduce a different type of corruption than they were originally meant
to cause:

  - the "bad node header" check originally mangled the 'type' member of
    the rdatasetheader_t structure for cname.example.nil,

  - the "bad node data" check originally mangled the 'serial' and
    'rdh_ttl' members of the rdatasetheader_t structure for
    aaaa.example.nil.

Update the offsets at which the map-format zone file is malformed at by
the "masterformat" system test so that the relevant checks fulfill their
original purpose again.