Fix sqlops memory leak in sql_avp_load / sql_avp_delete / sql_avp_store (for 3.5 and master)

[nikbyte]

Summary
This pull request fixes a memory leak in the sqlops module (function fixup_sql_avp) where a dynamically allocated string (sp->u.s.s) was not released in certain error paths or after normal fixup usage.

Details
When parsing script parameters for sql_avp_load() / sql_avp_delete() / sql_avp_store(), if the first parameter was a plain string (not prefixed by '$'), the code allocated memory for sp->u.s.s. However, it never got properly freed:

1. In the error path (goto err_free:), only sp was freed, leaving sp->u.s.s allocated.
2. In the success path, there was no custom fixup_free_* function to release sp->u.s.s.

Repeated calls thus caused incremental memory leaks.

Solution

1. Introduced a new free function fixup_free_avp_source() that properly frees both sp->u.s.s (if allocated) and the sp structure.
2. Updated the module to use this free function instead of the standard fixup_free_pkg().

By doing so, all allocated memory is correctly released, eliminating the leak.

Compatibility
No breaking changes or behavioral differences other than fixing the memory usage issue. No impacts on SIP interoperability or script compatibility.

[bogdan-iancu]

Thank you @nikbyte , I will backport this to 3.5 also