PHP: SERVER_PORT is hard coded to "80"

[ac000]

This is set in src/nxt_php_sapi.c

1373:    nxt_php_set_cstr(req, "SERVER_PORT", "80", 2, track_vars_array TSRMLS_CC);

Once the patch from https://github.com/nginx/unit/issues/753#issuecomment-1258842715 is committed we will be able to use the local_port member of the nxt_unit_request_t structure.

Despite the warming in the PHP reference guide we should probably at least try and get it right.