Use qualified member names in ODS sizeof expressions

[dand-oss]

Replace the null-pointer member expressions in maxPagesPerSCN and gensPerPage with sizeof(scns_page::scn_pages) and sizeof(generator_page::gpg_values).

This is a readability cleanup, not a runtime null-dereference fix: sizeof does not evaluate these operands. The full array types and resulting page-capacity arithmetic remain unchanged.

Validation on Linux x86-64 with GCC 16.2 / C++20:

• Compiled and linked the actual before/after ods.cpp with a focused harness and upstream's generated configuration headers.
• Static assertions verify equality of the old and new sizeof operands.
• Before/after results are identical for 4,096-, 8,192-, 16,384-, and 32,768-byte pages.
• git diff --check passes.

A full patched server build has not been completed locally.