t30_api.c missing backward compat feature `t30_set_supported_resolutions`

[rmackinnon]

Building OpalVOIP against v3.0.0 results in missing function:

spandsp_fax.cpp:938:7: error: ‘t30_set_supported_resolutions’ was not declared in this scope; did you mean ‘m_supported_resolutions’?
  938 |       t30_set_supported_resolutions(t30state, m_supported_resolutions);
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~